JP2004124248A - Ultra-fine metal particle, microbody and their production processes - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultra-fine metal particle which is safe, convenient and suitable for industrial use wherein a boron nitride coated film is deposited on the surface of a metal particle. <P>SOLUTION: The ultra-fine metal particle wherein the surface of the particle is coated with boron nitride is obtained by heat-treating a powder (powder a+b) wherein a powder (powder a) composed of an oxide of a transition metal oxide is mixed with a boron powder (powder b) in an atmosphere of nitrogen gas or ammonia gas or a mixed gas atmosphere containing at least one chosen from these at 800-1,700°C. Here, the particle has an average particle size of ≤1 μm and is composed of the transition metal or an alloy containing at least one transition metal. <P>COPYRIGHT: (C)2004,JPO

Description

【００８４】
【表２】

【００８５】
【表３】

【００８６】
（実施例３）
Ｎｉを含有するＦｅの酸化物の粉末５ｇと、ほう素粉５ｇをＶ型混合機に投入して混合した。この混合粉末をアルミナ製ボートに適量充填し、炉の中に配置し、流量が２（ｌ／ｍｉｎ）の窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１１００℃で２時間保持して室温まで炉冷した。熱処理後の粉末について観察したところ、窒化ほう素で表面を被覆した金属粒子を得た。組成分析したところ、金属粒子はＮｉを含有するＦｅであることがわかった。
【００８７】
（実施例４）
金属粒子とＢＮまたはＣ分離操作について説明する。図４は、ＢＮ被覆金属粒子およびＢＮ微小体の製造工程図を示すものである。被覆金属粒子を製造する場合、製造工程は図４のＳ１→Ｓ２→Ｓ３→Ｓ４となる。Ｓ２では原料の粉末を入れた窒化ほう素製ルツボ４２を管状炉４３中で熱処理した。Ｓ２で得られた熱処理粉末は被覆金属粒子と微小体の混合粉末４１であるため、被覆金属粒子はＳ３、Ｓ４の分離精製の工程を経て回収された。Ｓ３工程では、熱処理粉末をアセトンやエタノールなどの有機溶媒で代表される媒体４５中に分散させたものを洗浄槽４４で攪拌させ、被覆金属粒子を自然沈降させた。攪拌の手段として洗浄槽４４に超音波を印加すべく超音波洗浄装置４６を用いた。なお、超音波印加に代えて、ガラス棒による手動攪拌やペンシルミキサーなどの攪拌機を攪拌の手段として使用したところ、十分に攪拌することができた。
【００８８】
Ｓ４工程では、上澄み液４７を取り除いて沈殿物を乾燥させることにより被覆金属粒子４８が回収された。同時に上澄み液を乾燥させるとＢＮ微小体が回収された。上記工程ではＢＮ被覆金属粒子とＢＮ微小体を同時に得ることが出来た。特にＢＮ微小体のみを製造する場合、製造工程は図４のＳ１→Ｓ２→Ｓ５→Ｓ６としてもよい。Ｓ５工程は、塩酸や硫酸などの酸性溶液によって熱処理粉末中の金属粒子を溶解させる工程である。酸性溶液中に熱処理粉末を浸漬させた後、沈殿物を回収した。Ｓ６工程は、沈殿物を水洗した後、乾燥させる工程である。Ｓ５で得られた沈殿物に純水を適量注ぎ、ガラス棒などで攪拌した後、再び沈殿させて上澄み液を除去後、乾燥させることによりＢＮ微小体が得られた。酸性溶液の完全除去のために、Ｓ６工程は数回繰り返すことが好ましい。なお上記製造工程は炭素で被覆された金属粒子および炭素微小体を製造する工程にも適用することができた。
【００８９】
図５は、電子顕微鏡（ＴＥＭ）で観察した本発明に係る粒子構造の顕微鏡写真であり、ＢＮ被覆したＦｅ粒子を示している。図６は、図５の構造を模式的に説明するための概略図である。図６に示すように、Ｆｅ粒子１は周囲をＢＮ膜２で被覆されている。ＢＮ被膜の様子をさらに拡大した写真を図７に示す。
【００９０】
図７は、電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真であり、ＢＮ被覆したＦｅ粒子を示している。図８は、図７の構造を模式的に説明するための概略図である。図７に示すように、Ｆｅ粒子１の表面に被覆されたＢＮ膜には、積層された結晶格子の縞模様が認められる。格子面３の部分は、格子面がＦｅ粒子１の表面に沿って、複数の格子面がほぼ並行に積層されている。格子面４や格子面５の部分は、格子面同士が平行でない箇所を有するが、Ｆｅ粒子１の表面を十分に被覆していることがわかる。
【００９１】
（実施例５）
平均粒径０．０３μｍのα−Ｆｅ_２Ｏ_３粉（ａ粉末）５ｇと平均粒径２０μｍの炭素粉（ｂ粉末）５ｇとをＶ型混合機に投入して１０分間混合した。この混合粉末５１を窒化ほう素製ルツボ５２に適量充填し、管状炉５３内に前記ルツボ５２を設置して流量２ｌ／ｍｉｎの窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１０００℃で２時間保持して室温まで３℃／ｍｉｎの速度で炉冷した。管状炉の構造は図１７の概略図に示す。熱処理前後の各粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図９（熱処理前）および図１０（熱処理後）に示すような回折パターンが得られた。上記熱処理を施した粉末からは主にグラファイトの（００２）ピークとα−Ｆｅの（１１０）ピークを検出した。さらに上記熱処理後の粉末の磁気特性をＶＳＭ（試料振動型磁力計）にて測定した結果を表４に示す。飽和磁化は比較例４の値の１００倍程度であり、Ｘ線回折測定の結果と合わせてＦｅ_２Ｏ_３がＦｅに還元されていることがわかる。上記熱処理後の粉末をＰＣＴ試験機（プレッシャークッカーテスト試験機）にて湿度１００％、１２０℃、１気圧で２４時間曝した後、粉末の含有酸素量を金属中酸素・窒素・水素分析装置（堀場製ＥＭＧＡ−１３００）にて分析した。酸素量の分析結果を表５に示した。ＰＣＴ試験後も酸素量の増分がなく、Ｆｅ粉表面がグラファイト膜で被覆されていることを裏付ける。なお、上記金属中酸素・窒素・水素の分析は、黒鉛ルツボに試料粉末０．５ｇを充填し、ルツボを２０００〜３０００℃へ急速加熱することにより試料中のＯ，Ｎ，Ｈを熱分解し、ガスクロマトグラフと熱伝導度検出器により、発生したＣＯ_２，Ｎ_２，Ｈ_２Ｏガスを検出することによってＯ，Ｎ，Ｈの含有量を分析する方法である。
【００９２】
（比較例４）
熱処理温度を５００℃とした以外は実施例５と同様にして混合粉末を熱処理してＸ線回折、ＶＳＭ測定、ＰＣＴ試験を行なった。Ｘ線回折パターンは熱処理前後で変化がみられず、反応が進行していない。飽和磁化の値も殆ど変化していない。
【００９３】
（比較例５）
平均粒径０．０２μｍのＦｅ粉（真空冶金株式会社製超微粒子）を実施例５と同条件で耐食試験を行なった。飽和磁化は純鉄の値（約２６０×１０^−６ｗｂ・ｍ／ｋｇ）の３０％程度まで低下している。
【００９４】
【表４】

【００９５】
【表５】

【００９６】
図１１は、ＴＥＭ（透過型電子顕微鏡）で観察した実施例５に係る金属超微粒子の構造の顕微鏡写真である。ＴＥＭ観察するにあたり、必要とされる試料調整以外、粒子への損傷や変異などを与える加工は一切施していない。図１２は、図１１の構造を模式的に説明する概略図であり、若干拡大している。金属超微粒子１１は、α−Ｆｅの粒子１２の表面が全て所定の厚さのグラファイト薄膜２０で被覆された粒子である。この被覆はα−Ｆｅの粒子１２の表面を保護しており、効果的に酸化防止している。グラファイト薄膜２０の外側に散在する凸部２１，２１ｂは、グラファイトの異層が成長したものか、異物が付着したもののいずれかと推定される。α−Ｆｅの粒子１１自体の明暗のパターン１３ａ，１３ｂ，１３ｃは、α−Ｆｅの粒子１１の形状（略球形）に起因する干渉パターン（２点鎖線で表示）である。α−Ｆｅの粒子の両端では、グラファイト薄膜の境界１４が若干不明瞭に撮影されているため、点線で表示した。これは略球形の形状により全てに焦点を合わせることが難しいためであり、実際の形状が不明瞭になっている訳ではない。１点鎖線で輪郭を表示した領域は、金属超微粒子１１をＴＥＭ観察のサンプルホルダーに固定させるためのコロジオン膜１５である。符号１６の線と符号は、その３本線の長さが２０ｎｍに相当するスケールである。図１１を撮影した際のスケールをコピーして図１２に付け加えた。
【００９７】
図１３は、ＴＥＭ（透過型電子顕微鏡）で観察した本発明に係る粒子構造の顕微鏡写真であり、図１１の左下半分近傍を拡大してグラファイト薄膜２０の様子を説明するものである。図１３の構造を図１４の概略図で模式的に説明する。グラファイト薄膜２０は、グラファイトの結晶構造を主として構成されている。例えば、格子縞２０ａ，２０ｂ，２０ｃは、グラファイトの層状格子面を表しており、格子縞の間隔がほぼ等間隔であり、α−Ｆｅの粒子１２の表面に対してほぼ平行に配列している。
【００９８】
ただし、α−Ｆｅの粒子は球状であって、その表面には多少の凹凸があることから、グラファイト薄膜の一部には、格子縞２０ｆのようにα−Ｆｅの粒子１２の表面に対して傾斜している箇所もある。格子縞２０ｆは他の格子縞２０ｅを派生し、さらに、格子縞２０ｄとなっている。線の図示を省略したが、格子縞２０ｄはα−Ｆｅの粒子１２の表面に対してほぼ平行に配列している。このように、グラファイト薄膜には、層状格子面の配列の向きが変化したり、配列の状態が不鮮明になる箇所（梨地模様に見える箇所）が存在するが、隣接する結晶構造同士で整合を取ったり、α−Ｆｅの粒子１２の表面に対して結晶構造の面が平行になるように成長するために、ほぼ均一なグラファイト薄膜の被覆が構成されている。
【００９９】
図１４のグラファイト薄膜２０において、格子縞の一部を実線や点線で模式的に図示している。図示を省略しているが、空白の部分にも結晶構造は存在する。また、α−Ｆｅの粒子１２の表面とグラファイト薄膜２０の間には、中間層２５があると推定されるが、その詳細は図１５及び図１６にて説明する。
【０１００】
図１５は、ＴＥＭ（透過型電子顕微鏡）で観察した本発明に係る粒子の構造の顕微鏡写真であり、図１３のグラファイト薄膜２０近傍をさらに拡大した写真である。図１６は、図１５の構造を模式的に説明する概略図であり、若干拡大している。α−Ｆｅの粒子１２では、矢印ａの向きに沿って格子縞２４が見られ、α−Ｆｅの特有の結晶面を示している。Ｆｅ原子の並びが数珠つなぎになっている様子を克明に模写することは難しいので、点線で表示した。α−Ｆｅの粒子１２の表面近傍では、前記の矢印ａに沿った格子縞が崩れているが、その配列の端が平坦な面を構成しており、グラファイトの結晶が徐々に成長していく起点（グラファイトの成長層）となっている。以下、これらの領域を中間層２５と称する。中間層２５を経てグラファイト薄膜２０は成長し、形成される。
【０１０１】
図１６に示すように、α−Ｆｅの粒子１２の表面が比較的滑らかな球面（平坦面）であれば、グラファイトの層状格子面２２は矢印ｄに沿った面となり、規則的に平行に配列しながら成長するため、緻密で非常に薄い被覆を構成する。ここで、緻密とは規則的な格子面が積層している部分を有することを指す。矢印ｄに垂直な方向に、層状格子の面が、１５〜１７層積層して非常に薄く被膜を構成していた。中間層２５の厚さは、グラファイトの層状格子面２２の間隔で言うと、１〜２層に見える。成長し始めたグラファイトの結晶面も中間層に含めると、中間層１５の厚さは、グラファイトの層状格子面２２の間隔でいうと、２〜４層程度である。
【０１０２】
転位した箇所２３は、結晶成長にズレが生じ、結晶構造が不連続化した部分と推定される。層状格子が成長して積層構造となるときに、格子の欠陥に起因して、ある部分の成長が１層分遅れたとする。ある部分の成長が再開されたとき、ある部分のｎ−１層目の格子面と隣接する部分のｎ層目の格子面が結合して１つの面（転位した面）を構成することがある。転位した面の発生率は高くなく、被膜全体でみると均一で緻密な薄膜といえる。なお、グラファイト薄膜２０の表面には凸部２１ｂが存在するが、図１６の写真では鮮明には撮影されなかったため、それらしき箇所を点線で表示した。
【０１０３】
（実施例６）
平均粒径０．０３μｍのヘマタイト（Ｆｅ_２Ｏ_３）粉末３ｇと平均粒径２６μｍのほう素粉末７ｇをＶ型混合機に投入して１０分間混合した。この混合粉末１２１を窒化ほう素製の坩堝１２２に充填して管状電気炉１２３に設置し、流量２（ｌ／ｍｉｎ）の窒素ガス気流中で、室温から３（℃／ｍｉｎ）の速度で昇温した後、１１００℃で２時間保持して室温まで炉冷した。熱処理前の混合粉末は赤黒色であったが、熱処理後の粉末は灰白色に変色していた。熱処理後の粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図１７に示すような回折パターンが得られ、上記熱処理を施した粉末からは六方晶の窒化ほう素（ｈ−ＢＮ）と菱面体の窒化ほう素（ｒ−ＢＮ）、およびα−Ｆｅの回折ピークを検出した。窒化ほう素とＦｅを分離するため、アセトン５００ｃｃ（０．５×１０^−３ｍ^３）の中に上記粉末５ｇを投入して５分間超音波洗浄を施し、上澄み液と沈殿物を分離した。上澄み液１２７をドラフト内で更に２４時間放置してアセトンを乾燥させ、窒化ほう素粉末１２８（重量６ｇ）を回収した。
【０１０４】
この窒化ほう素粉末を透過型電子顕微鏡（ＴＥＭ）にて観察したところ、図１９の写真に示すようなワイヤ状の組織が観察された。格子像を解析すると、この窒化ほう素ワイヤは菱面体構造であった。流量の単位は（ｌ／ｍｉｎ）≒約１６．７×１０^−６（ｍ^３／ｓ）に相当する。実施例６の製造工程は、粉末混合工程（Ｓ１１）、雰囲気中熱処理工程（Ｓ１２）、粉末を分散させた媒体への超音波印加工程（Ｓ１３）、窒化ほう素微小体の分離・乾燥工程（Ｓ１４）を有し、図２２の工程フローと概略図に対応する。同図中、符号１２４は洗浄槽、符号１２６は超音洗浄機、符号１２５は熱処理後の粉末を分散させた溶媒（アセトン）に相当する。なお、生成した粒子を分散させるべく超音波を印加できるのであれば、洗浄機に限らず使用することができる。
【０１０５】
図２０は、図１９の写真の構造を模写した概略図であり、ワイヤ状の窒化ほう素微小体を示す。この窒化ほう素微小体１０１は、内部に空洞１０２を有するチューブ１０３が多数個連結して、長い屈曲したチューブ状を構成している。一方の端はチューブ１０３の構造で終端されている。他方の端は、チューブ１０３であるｒ−ＢＮ組織と、ｈ−ＢＮ的な部位１１２ｂが混在した組織を経て、ｈ−ＢＮ組織１１２で終端されている。図２０中、点線で表示した曲線は、電子顕微鏡のサンプルホルダーに窒化ほう素微小体１０１を固定するためのコロジオン膜の外延を表している。図２０の方形の囲いの右外の線と文字は、線の長さが２００ｎｍの寸法に対応することを示す。
【０１０６】
図２１は、図２０中の窒化ほう素チューブのみを抜粋・拡大した概略図である。チューブの先端近傍１１１は、チューブの途中の部分と重なって見えており、明瞭ではない為に先端が閉鎖されているかは定かでない。この先端近傍から、空洞１０２とそれを囲うチューブ１０３の構造が続いており、途中、チューブ間の節１０４と考えられる部位や、チューブの厚さが厚いか斜めに観察する為に厚く見える箇所と考えられるコブ１０５が存在する。連続するチューブの向きは、例えば屈曲部１１０で大きく屈曲しているように見える。チューブの厚さは必ずしも一様に見えておらず、コブ１０５や節だけでなく、複雑な線や脈理に見える構造を伴いながら空洞１０２を形づくっている。チューブ構造は先端近傍１１１から節１０４ｂまで明瞭に観察され、チューブの直径は０．１２〜０．２０μｍ（１２０〜２００ｎｍ）である。この辺りは結晶組織が複雑であるため、ｒ−ＢＮとｈ−ＢＮが混在しているか、混相となっていると推測される。異相の混在は、チューブの屈曲と関係すると考えられる。明瞭にパイプ状に見えるチューブ１０３の結晶構造を拡大観察すると、原子の並びが３層周期を繰り返すｒ−ＢＮとなっており、その周期の繰り返し方向は、チューブの直径方向を向いている。
【０１０７】
（実施例７）
平均粒径０．０３μｍのα−Ｆｅ_２Ｏ_３粉（ａ粉末）５ｇと平均粒径２０μｍの炭素粉（ｂ粉末）５ｇとをＶ型混合機に投入して１０分間混合した。この混合粉末２５１を窒化ほう素製ルツボ２５２に適量充填し、管状炉２５３にて流量２ｌ／ｍｉｎの窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１０００℃で２時間保持して室温まで３℃／ｍｉｎの速度で炉冷した。流量の単位は（ｌ／ｍｉｎ）≒約１６．７×１０^−６（ｍ^３／ｓ）に相当する。
【０１０８】
熱処理前後の各粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図２３（熱処理前）および図２４（熱処理後）に示すような回折パターンが得られた。上記熱処理を施した粉末からは主にグラファイトの（００２）ピークとα−Ｆｅの（１１０）ピークを検出した。図２４にて、○印はグラファイトの結晶構造に対応するピークであり、■印はα−Ｆｅの結晶構造に対応するピークであり、横軸は回折角度の２θ（°）、縦軸は回折Ｘ線の強度（ｃｐｓ）である。グラファイトの最大強度のピークは半値幅が約０．２°となっており、熱処理後の粉末の結晶性はよい。さらに、図２３と図２４に対応した熱処理前後の粉末について磁気特性をＶＳＭ（試料振動型磁力計）にて測定した所、飽和磁化は前者で１．３０×１０^−６Ｗｂ・ｍ／ｋｇ、後者で１３１×１０^−６Ｗｂ・ｍ／ｋｇであった。以上より、Ｆｅ_２Ｏ_３がＦｅに還元されていることがわかる。
【０１０９】
上記熱処理後の粉末をＴＥＭ（透過型電子顕微鏡）観察した所、図２５に示すようなチューブ状の微小体が確認された。図２５は電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。ＥＤＸ（エネルギー分散型Ｘ線検出器）による組成分析の結果、微小体の先端の黒色粒子はＦｅであり、チューブはＣ（炭素）であることが判明した。
【０１１０】
図２６は、図２５の写真の構造に対応する概略図である。炭素微小体２０１は、Ｆｅ粒子２０２をベースにして炭素のチューブ２０３が曲線状に成長した構造である。チューブ２０３の内部には複数の節２０４が存在し、対向する節とチューブの壁２０３ｂに囲われた領域は空洞２０５を構成する。チューブ２０３の他端は閉じられており、先端部２０６となっている。この炭素微小体２０１において、チューブの成長方向が曲がっていることは、チューブの壁の厚さや節の間隔が均一ではないことと関係すると考えられる。特に、チューブの壁２０３ｃ，２０３ｅの箇所はチューブの厚さが薄い。
【０１１１】
もう一つの炭素微小体２０７は、Ｆｅ粒子２０８をベースにして炭素のチューブ２０９が曲線状に成長するとともに、先端に他のＦｅ粒子２１３を包含する構造である。チューブ２０９の内部には複数の節２１０が存在し、対向する節とチューブの壁に囲われた領域は空洞２１１を構成する。Ｆｅ粒子２１３の近傍にあるＦｅ粒子２２０はチューブの壁２２０等により隔てられているように見える。この炭素微小体２０７にて、Ｆｅ粒子２１３はチューブの成長当初から付いていたものか、チューブが成長した過程で取り込んだものかは定かでない。なお、Ｆｅ粒子２０８やチューブの壁２１２は、炭素微小体２０１と重複して見えているだけで、接続はされていない。さらに、他のＦｅ粒子２１４は単独で存在している。同図中、直線若しくは屈曲した一点鎖線は原料の炭素２１５，２１６の輪郭を表している。曲線状の一点鎖線は炭素微小体等を電子顕微鏡のサンプルホルダーに固定するためのコロジオン膜２１７，２１８の輪郭を表している。符号２１９は、図２６の寸法を判りやすくするために記入したスケール表示であり、元の図２５にそのような構造がある訳ではない。スケール表示の３本線の長さは１００ｎｍに相当する。
【０１１２】
図２５の写真に基づいて、各々の炭素微小体の外径Ｒｏと内径Ｒｉの比を測定した。任意の箇所について測定し、（Ｒｉ／Ｒｏ）＝０．６７、０．７５、０．４０、０．６９、０．５７、０．６３、０．７５、０．４４というようなデータを得た。実施例８の条件を変えて炭素微小体を製造すると、平均外径や平均内径も変えることができることができた。これらの条件変更を考慮すると、（Ｒｉ／Ｒｏ）の上限を０．８とすることができる。
【０１１３】
図２７は、電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。図２５において、Ｆｅ粒子２０２とチューブ２０３の接合箇所の近傍を拡大したものである。図２８は、図２７の写真の構造に対応する概略図である。なお、図２８は、説明し易くするために、図２７の結晶組織の主要な部分のみを実線や点線に代えて表現した。従って、点線でハッチングした領域の周囲が空白であったとしても、その部分は記載を省略しているだけである。
【０１１４】
図２８によると、Ｆｅ粒子２０２では、ほとんどの領域で特定の結晶面に沿った表面を有するように見える組織となった。以下、Ｆｅ主相２２０，２２１と称する。Ｆｅ主相２２０の左側には、配列の面の向きが異なる相２２５や、梨地模様に見える異相２２６などが観察された。なお、平行に配置した点線でＦｅ主相２２０等を表現したが、点間隔や線間隔は必ずしも図２７と一致するものではない。線の配列の向き等を判り易く説明するために描いたものである。
【０１１５】
図２８中の炭素のチューブについて説明する。仮想的な境界線２２７およびＦｅ主相２２１から先にはチューブ２０３が生成されている。筒状のチューブの壁の中が節２３６、２３９で仕切られた構造であることが判る。節２３６とＦｅ粒子２０２とチューブの壁で囲われた領域、または節２３６，２３９とチューブの壁で囲われた領域は空洞となった。
【０１１６】
チューブの壁は、結晶の配列がグラファイト構造的な相を主として構成されている。以下、グラファイトとそれに類似の組織を併せてグラファイト相と称する。グラファイト相は、結晶の配列が特定の面に沿って積層したように見えるという点で、Ｆｅよりも明瞭である。チューブの壁の成長方向に対してグラファイト相２３０，２３１，２３２，２３３，２３７，２３８，２４０の面は、平行若しくは略平行と言える。これらに対して、節２３６，２３９ではグラファイト層の面は、チューブの壁の成長方向に対して直交若しくは略直交と言える。節２３６の左側の付け根では、グラファイト層の向きが下向きの層２３４と上向きの層２３５にＹ字状に分かれており、樹木の幹と枝の如き組織を呈している。節２３９の付け根はチューブの壁にほぼ直交しており、節の組織は少なくとも２通りあると考えられる。グラファイト相２４２は架橋もしくは節と考えているが、他の構造体のグラファイト相２４２が紛れこんでいるため、断定はできない。
なお、グラファイト層の原子配列の積層の様子は、グラファイト層２３５，２３８や節２３６，２３９に表現したように間隔が狭い。全ての層を同様に図示すると複雑になるため、他の部分では層の数を減らして図示した。また、一層一層が明瞭に判る場合には線で図示したが、途切れ途切れで続いているように見える場合には、点線で表示した。
【０１１７】
上記熱処理後の粉末５ｇをアセトン５００ｃｃの中に投入して５分間超音波洗浄を施し、上澄み液と沈殿物を分離した。上澄み液２５７をドラフト内で更に２４時間放置してアセトンを乾燥させ、炭素微小体の粉末２５８を得た。粉末２５８は粗大遷移金属粒子等を除くことにより、炭素微小体の割合を向上させたものである。
【０１１８】
実施例７の製造工程は、粉末混合工程、雰囲気中熱処理工程、粉末を投入した媒体への超音波印加（分散工程）、粗大遷移金属粒子などの分離および乾燥工程を有し、図２９の工程フローと概略図に対応する。同図中、符号２５４は洗浄槽であり、符号２５５は熱処理後の粉末を分散させた溶媒（アセトン）であり、符号２５６は超音波洗浄装置に相当する。なお、生成した各粒子を溶媒中に分散させるべく超音波を印加できるものであれば、洗浄装置に限らず使用することができる。
【０１１９】
【発明の効果】
以上説明したように、本発明の金属超微粒子およびその製造方法を用いることにより、安全且つ簡便で工業的利用に適した被膜を金属粒子表面に付与した金属超微粒子を得ることができる。さらに、金属超微粒子を製造する際に副生成物に係る微小体とその製造方法を得ることができる。
【図面の簡単な説明】
【図１】熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図２】熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図３】Ｆｅ_２Ｏ_３とＢが反応することにより、窒化ほう素被覆Ｆｅ粒子等が生成する反応過程を説明する概略図である。
【図４】窒化ほう素被覆金属粒子および窒化ほう素微小体の製造工程図である。
【図５】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図６】図５の構造を模式的に説明するための概略図である。
【図７】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図８】図７の構造を模式的に説明するための概略図である。
【図９】熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図１０】熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図１１】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１２】図３の構造を模式的に説明するための概略図である。
【図１３】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１４】図５の構造を模式的に説明するための概略図である。
【図１５】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１６】図７の構造を模式的に説明するための概略図である。
【図１７】実施例１の製造工程で用いる管状炉の概略図である。
【図１８】本発明の粉末のＸ線回折パターンを示すグラフである。
【図１９】電子顕微鏡で観察した本発明に係る粒子構造の写真である。
【図２０】図１９の写真の構造に対応する概略図である。
【図２１】図２０の一部を拡大した概略図である。
【図２２】実施例６の製造工程を説明するフロー及び概略図である。
【図２３】熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図２４】熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図２５】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図２６】図２５の写真の構造に対応する概略図である。
【図２７】電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図２８】図２７の写真の構造に対応する概略図である。
【図２９】実施例７の製造工程を説明する工程フロー及び概略図である。
【符号の説明】
１　Ｆｅ粒子、　２　ＢＮ被膜、　３　格子面、　４　格子面、
５　格子面、
１１　金属超微粒子、　１２　α−Ｆｅの粒子、
１３ａ　１３ｂ　１３ｃ　パターン、
１４　グラファイト薄膜の境界、　１５　コロジオン膜、
１６　スケール、　２０　グラファイト薄膜、
２０ａ　２０ｂ　２０ｃ　格子縞、
２０ｅ　格子縞、　２０ｄ　格子縞、　２０ｆ　格子縞、
２１　２１ｂ　凸部、
２２　層状格子面、
２３　転位した箇所、　２４　格子縞、
２５　中間層、　２７　グラファイトの成長層、
４１　混合粉末、　４２　窒化ほう素製ルツボ、　４３　管状炉、
４４　洗浄槽、　４５　媒体、　４６　超音波洗浄装置、
４７　上澄み液、　４８　被覆金属粒子、
５１　混合粉末、　５２　窒化ほう素製ルツボ、　５３　管状炉、
１０１　窒化ほう素微小体、　１０２　空洞、　１０３　チューブ、
１０４　１０４ｂ　節、
１０５　コブ、　１１０　屈曲部、　１１１　先端近傍、
１１２　ｈ−ＢＮ組織、　１１２ｂ　ｈ−ＢＮ的な部位、
１１３　コロジオン膜、　１２１　混合粉末、　１２２　坩堝、
１２３　管状電気炉、　１２７　上澄み液、　１２８　窒化ほう素粉末、
２０１　炭素微小体、　２０２　Ｆｅ粒子、　２０３　チューブ、
２０３ｂ　チューブの壁、
２０３ｃ　２０３ｅ　チューブの壁、
２０４　節、　２０５　空洞、　２０６　先端部、
２０７　炭素微小体、　２０８　Ｆｅ粒子、　２０９　チューブ、　２１０　節、
２１１　空洞、　２１２　チューブの壁、　２１３　Ｆｅ粒子、
２１４　Ｆｅ粒子、
２１５　２１６　原料の炭素、
２１７　２１８　コロジオン膜、
２１９　スケール表示、　２２０　Ｆｅ粒子、
２２０　２２１　Ｆｅ主相、
２２４　２２７　仮想的な境界線、
２２５　配列の面の向きが異なる相、　２２６　梨地模様に見える異相、
２３０　２３１　２３２　２３３　２３７　２３８　２４０　グラファイト相、
２３４　２３５　グラファイト相、
２３６　２３９　節、
２４１　グラファイト相、　２４２　他の構造体のグラファイト相、
２５１　混合粉末、　２５２　窒化ホウ素製ルツボ、　２５３　管状炉、
２５４　洗浄槽、　２５５　熱処理後の粉末を分散させた溶媒、
２５６　超音波洗浄装置、　２５７　上澄み液、　２５８　炭素微小体の粉末[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a metal particle used as a raw material of a magnetic recording medium such as a magnetic tape or a magnetic recording disk, or an electronic device (a soft magnetic body such as a yoke) such as a radio wave absorber, an inductor, and a printed circuit board, and a method of manufacturing the same. Further, the present invention relates to a microparticle which is a by-product when forming metal particles and a method for producing the microparticle.
[0002]
[Prior art]
As electronic devices become smaller and lighter, the raw materials constituting the electronic devices themselves are required to be reduced in size to nanometers. At the same time, high performance devices must be realized. For example, for the purpose of improving the magnetic recording density, it is required to simultaneously make the magnetic particles coated on the magnetic tape nano-sized and to improve the magnetization.
[0003]
Conventionally, ferrite powder has been mainly used for magnetic recording media, but has a problem that magnetization is small and signal intensity is low. In order to obtain sufficient output characteristics, metal magnetic particles represented by Fe and Co are suitable. For example, if the particle diameter is reduced to 1 μm or less for higher recording density, the metal particles are less susceptible to oxidation. Since it is active, the oxidation reaction proceeds violently in the atmosphere, and some or all of the metal is transformed into an oxide and the magnetization is reduced. In order to improve the handling of fine metal particles, a method of coating the surface of magnetic particles containing Fe and Co with a ferrite layer (for example, Patent Document 1) and a method of coating the surface of Fe powder with graphite (for example, Patent Document 2) ) Etc. have been proposed.
[0004]
In the case of metal particles having a particle size of 1 μm or less as in the above example, a coating is applied to the surface of the particles so that the particles do not directly contact the atmosphere (oxygen) in order not to impair the function as a metal. It is essential. However, the method of covering the surface with a metal oxide as in Patent Literature 1 oxidizes and deteriorates the metal to a considerable extent.
Further, when metal particles are coated with graphite as in Patent Document 2, in order to form a state in which metal melts carbon, heat treatment must be performed at an extremely high temperature of 1600 ° C. to 2800 ° C. No. Carbonization of metal and CO of graphite₂Is concerned. As a coating method that solves these problems, there is a method of coating metal particles with boron nitride (BN) (for example, Non-Patent Document 1). BN is a material used for a “crucible” and has a high melting point of 3000 ° C., excellent thermal stability, and low reactivity with metals. In addition, it has an insulating property. The method of providing the metal particles with the BN coating includes (1) heating the mixed powder of metal and B by arc discharge in a nitrogen atmosphere, or (2) heating the mixed powder of metal and B in a mixed atmosphere of hydrogen and ammonia. Heating or (3) heat treating a mixture of metal nitrate, urea and boric acid in a hydrogen atmosphere.
[0005]
[Patent Document 1]
JP-A-2000-30920 (pages 9 to 11, FIG. 2)
[Patent Document 2]
JP-A-9-143502 (pages 3 and 4, FIG. 5)
[Non-patent document 1]
"International Journal of Inorganic Materials 3 2001", 2001, p. 597
[0006]
[Problems to be solved by the invention]
In the above methods for producing a BN film, since the production methods (1) and (2) use metal particles as a raw material, there is a danger of ignition due to a rapid oxidation reaction, particularly when handling ultrafine particles having a particle diameter of 1 μm or less. In the production method (3), since the metal nitrate is thermally decomposed, a toxic gas (NO_x) Occurs. In addition, the method using the arc discharge in the production method (1) is not suitable for industrial use because the reaction temperature is as high as 2000 ° C. in addition to the low throughput and low productivity. Further, the hydrogen gas used in the production methods (2) and (3) has a risk of explosion, and is not preferably used industrially. Further, the coated metal particles obtained by the conventional technique have a problem that a part of the metal particles is modified to cause deterioration of saturation magnetization.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have conducted intensive studies on metal ultrafine particles in which a film suitable for industrial use is coated on a metal particle surface by a safe and simple method and a method for producing the same. As a result, the present invention has been completed. I came to.
[0008]
[1] The ultrafine metal particles of the present invention are metal particles obtained by reducing a metal oxide, and the surfaces of the metal particles are coated with boron nitride and have an average particle size of 1 μm or less. There is a feature. Desirably, the average particle size is in the range of 0.001 to 1 μm. For example, ultrafine metal particles having an average particle diameter of 0.2 to 0.5 μm and excellent in oxidation resistance can be obtained. More preferably, the average particle size is from 0.01 μm to 0.1 μm. When the particle diameter is 0.1 μm or less, the effect of preventing oxidation by coating the surface with boron nitride is particularly prominent.
[0009]
The average particle diameter can be determined, for example, by dispersing the sample powder in a solvent, irradiating a laser beam, and measuring the average particle diameter using diffraction (first method). Alternatively, it can be determined by an air permeation method (for example, a Fischer-sub-sieve sizer (FSSS) method) (second method). In order to obtain high measurement accuracy, it is preferable to use a commercially available measurement device using the first method. When the average particle size is difficult to measure with the first and second methods because the amount of the sample is very small, the sample is observed with an electron microscope to measure the average particle size (the third method). ). For example, take an electron micrograph of the sample. Measure the average particle size of the metal ultra-fine particles in an arbitrary area in the photograph and calculate the average value, or draw a line segment of any length in the photograph and measure the length of the part that crosses the particle of the line segment The average particle diameter is determined as L / N from the sum L of the particles and the number N of the particles crossed by the line segment. However, in the third method, an average value of at least 50 or more particles is obtained.
[0010]
In the present invention, it is desirable that all of the fine particles are coated with boron nitride (or carbon), but it is not always necessary that all of the particles are coated. Further, the surface of the ultrafine particles is desirably coated with boron nitride (or carbon), but need not necessarily be composed of only particles whose surface is completely coated with boron nitride (or carbon). The description of the numerical range in the specification and the claims of the present application is, for example, a description that "the particle size is 0.001 to 1 μm" means "the particle size is in the range of 0.001 μm or more and 1 μm or less." Is used as equivalent to the expression
[0011]
[2] In the above [1], the metal oxide is an oxide containing a transition metal. The metal particles are desirably selected from Fe, Ni, Co, and an alloy containing at least one of them. Examples include Fe particles coated with boron nitride, Ni particles coated with boron nitride, FeNiCo particles coated with boron nitride, NiFe particles coated with boron nitride, and the like.
[0012]
[3] In the ultrafine metal particles according to the above [1] or [2], the boron nitride has a mainly h-BN crystal structure.
[0013]
[4] In the ultrafine metal particles according to any one of [1] to [3], the boron nitride is a film having a thickness of 100 nm or less. Here, the film thickness corresponds to the distance between the surface of the particle to be coated and the surface of the thin film to be coated. More preferably, the thickness can be reduced to 20 nm or less.
[0014]
[5] In the metal ultrafine particles according to any one of the above [1] to [4], the boron nitride has a crystal lattice plane or a lamination plane of two or more layers. More preferably, the film has a lattice plane or a lamination plane of four or more layers. Here, it is preferable that boron nitride is mainly composed of hexagonal crystal, and the lattice plane or lamination plane of the crystal is a hexagonal c-plane (that is, (002) plane). It is preferable that the lattice plane or the lamination plane of the crystal is formed along the plane of the metal particles.
[6] In the above item [5], an intermediate phase may be provided in the particles or boron nitride.
[0015]
[7] In any one of the above [1] to [6], the main component of the metal superparticle is a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is the saturation magnetization of the magnetic metal element. 10% or more and less than 100%. With respect to the above [7], when the core of the ultrafine metal particles is composed of magnetic particles, the boron nitride film covering the nuclei can be made extremely thin, 30 nm or less. Therefore, the volume ratio occupied by the magnetic particles in the ultrafine metal particles can be increased, and the decrease in the saturation magnetization of the ultrafine metal particles can be suppressed as compared with the related art. In a particle composed of a transition metal or an alloy containing a transition metal, a boron nitride film is coated on the particle when the saturation magnetization inherent to the material of the main component responsible for the magnetic property of the particle is set as a reference (ie, 100%). The saturation magnetization of the ultrafine metal particles can have a magnitude of 10% or more with respect to the above reference.
[0016]
[8] In any one of the above [1] to [7], after heat-treating under the conditions of 100% humidity, 120 ° C, 1 atmosphere and 24 hours, heat-treat the oxygen content (mass%) before heat treatment. The subsequent mass increment of oxygen is not more than 50%. Even if the surface of the ultrafine metal particles is not completely covered with the boron nitride film, that is, even if the coating is locally thinned, it can be used. However, since it is difficult to prevent the progress of oxidation during long-term storage, it is desirable to completely cover the surface of the ultrafine particles with a boron nitride film.
[0017]
In the specification and the claims of the present application, mass%, that is, mass percentage (% by mass) indicates a composition ratio by mass of a substance. That is, it indicates how much each elemental component is contained with respect to the unit mass of the metal ultrafine particle.
The method of measuring the mass% of each composition is, for example, to rapidly decompose oxygen and the like in the sample by rapidly heating the sample powder to 2000 to 3000 ° C., and to generate oxygen gas by a gas chromatograph and a thermal conductivity detector. Alternatively, it is a method of analyzing the oxygen content by detecting an oxygen-containing gas. Since the metal ultrafine particles according to the present invention are particularly excellent in oxidation resistance, even if the above-described humidification / heating treatment is performed, an increase in the oxygen mass after the treatment relative to the oxygen content before the treatment is suppressed. .
[0018]
The magnetic particles may contain impurities or unavoidable impurities (elements originally contained in the raw materials) contained in the mixing of the raw materials to such an extent that the magnetic characteristics are not extremely deteriorated.
In the X-ray diffraction pattern, at least one of the peak having the highest intensity (Intensity (cps)) and the second peak having the highest intensity (intensity (cps)) is an element constituting the metal particle (excluding the coating). ) Peaks. More preferably, the peak of the oxide of the element (excluding BN) constituting the particles is sufficiently smaller than the third highest peak or not detected at all.
[0019]
[9] The method for producing ultrafine metal particles according to the present invention is characterized in that a powder obtained by mixing a powder containing a metal oxide and a powder containing boron is heat-treated in an atmosphere containing nitrogen, whereby the ultrafine metal particles are produced. In the method for manufacturing, the ultrafine metal particles are metal particles coated with boron nitride. The metal oxide preferably contains a transition metal (more preferably, it is composed of a transition metal oxide). The metal particles coated with the generated boron nitride preferably have an average particle diameter of 1 μm or less. The “atmosphere containing nitrogen” corresponds to an atmosphere selected from a mixed gas of an inert gas such as nitrogen gas and argon and a nitrogen gas.
[0020]
In the production method of the above [9], more preferably, a powder obtained by mixing particles containing iron oxide and particles containing boron is heat-treated in an atmosphere containing nitrogen to reduce the iron oxide to at least one of iron and an iron boron compound. By reducing to seeds to produce boron oxide, it finally produces at least one type of particle of iron or iron nitride, the surface of which is coated with boron nitride. And
[0021]
The method for producing ultrafine metal particles according to the above [9] is characterized in that the step of reducing the metal oxide particles and the step of coating the surfaces of the metal particles with a boron nitride film are performed in one heat treatment step. The production method of the present invention is superior to the production method of the comparative example described later in that it hardly contains oxygen. The manufacturing method of the comparative example is that, after producing ultrafine metal particles, an inert atmosphere containing oxygen at a low concentration is gradually supplied to the ultrafine metal particles in order to avoid spontaneous ignition and combustion (oxidation). This is a method for producing ultrafine particles that forms a thin oxide film on the surface.
[0022]
[10] In the above [9], the heat treatment is performed at a temperature of 800 ° C or higher. More preferably, it is carried out within the range of 800 to 1700 ° C.
[0023]
[11] The other ultrafine metal particles of the present invention are metal particles obtained by reducing a metal oxide, wherein the surfaces of the metal particles are coated with carbon and have an average particle diameter of 1 μm or less. There is a feature. Desirably, the average particle size is in the range of 0.001 to 1 μm. For example, ultrafine metal particles having an excellent oxidation resistance such as an average particle diameter of 0.2 to 0.5 μm can be obtained. More preferably, the average particle size is from 0.01 μm to 0.1 μm. When the particle size is 0.1 μm or less, the effect of preventing oxidation by coating the surface with carbon is particularly prominent.
[0024]
[12] In the above [11], the metal oxide is an oxide containing a transition metal. The metal particles are desirably selected from Fe, Ni, Co, and an alloy containing at least one of them. Examples include Fe particles coated with carbon, Ni particles coated with carbon, FeNiCo particles coated with carbon, NiFe particles coated with carbon, and the like.
[13] In the ultrafine metal particles according to the above [11] or [12], the carbon is mainly composed of graphite. Further, the carbon may have a crystalline structure of graphite and amorphous, and may be mainly composed of graphite.
[0025]
[14] In the ultrafine metal particles according to any one of [11] to [13], the carbon has a thickness of 100 nm or less. More preferably, the thickness can be reduced to 20 nm or less.
[0026]
[15] In the metal ultrafine particles according to any one of the above [11] to [14], the carbon is characterized in that the lattice plane or the lamination plane of the crystal is two or more layers. More preferably, the film has a lattice plane or a lamination plane of four or more layers. Here, it is preferable that carbon is mainly composed of graphite, and the lattice plane or lamination plane of the crystal is a lamination plane of graphite. It is preferable that the lattice plane or the lamination plane of the crystal is formed along the plane of the metal particles.
[16] In the above-mentioned [15], an intermediate phase may be provided in the particles or carbon.
[0027]
Since the carbon constituting the coating is mainly graphite in which the lattice planes are arranged in layers, the carbon has a plurality of planes of a layered lattice in which six-membered rings are connected. That is, it has a plurality of crystal lattice planes. The lattice plane of the layered lattice may have a laminated structure with respect to the surface of the particle. Since the interface between the particles and the coating has an intermediate layer or a region where transition metal and carbon are mixed or a crystal matching region of both, forming the surface of the layered lattice in at least two layers suppresses oxidation of the particles. It is desirable in doing. The plane of the layered lattice (lattice plane) can be formed, for example, in the range of 4 to 20 layers. The intermediate phase refers to a portion or boundary region of an intermediate structure between the crystal structure of the metal particles and the crystal structure of the coating. The thickness of the intermediate phase is about 1 to 5 layers of graphite lattice spacing or graphite layer. When the intermediate phase is thin, it is considered that the crystal lattice mismatch between the particles and the carbon film is alleviated and eliminated in a short distance, and the entire surface of the particles can be uniformly coated with the carbon film.
[0028]
[17] In any one of the above [11] to [16], the main component of the metal superparticle is a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is the saturation magnetization of the magnetic metal element. 10% or more and less than 100%. Regarding the above [17], when the core of the ultrafine metal particles is composed of magnetic particles, the carbon film coated can be extremely thin, having a thickness of 30 nm or less. Therefore, the volume ratio occupied by the magnetic particles in the ultrafine metal particles can be increased. As compared with the prior art, it is possible to suppress a decrease in the saturation magnetization of the ultrafine metal particles. Ultrafine metal particles in which a carbon film is coated on a particle composed of a transition metal or an alloy containing a transition metal, based on the saturation magnetization inherent to the material of the main component of magnetism (ie, 100%). May have a magnitude of 10% or more with respect to the reference.
[0029]
[18] In any one of the above [11] to [17], after heat-treating under the conditions of 100% humidity, 120 ° C, 1 atm, and 24 hours, heat-treat the mass of oxygen (mass%) before heat treatment. The subsequent mass increment of oxygen is not more than 50%. Even if the surface of the ultrafine metal particles is not completely covered with the carbon film, that is, even if the coating is locally thinned, it can be used. However, since it is difficult to prevent the progress of oxidation during long-term storage, it is desirable to completely cover the surface of the ultrafine particles with a carbon film.
[0030]
The magnetic particles may contain impurities and unavoidable impurities (elements originally contained in the raw materials) contained in the mixing of the raw materials to such an extent that the magnetic characteristics are not extremely deteriorated. In the X-ray diffraction pattern of a particle made of a metal or an alloy, the first or second highest intensity (Intensity (cps)) peak is the peak corresponding to the main element of the particle or the peak of graphite. Desirably. More preferably, the peak of the oxide of the element (excluding carbon) constituting the particles is sufficiently smaller than the third highest peak appearing in the X-ray diffraction pattern, or is not detected at all.
[0031]
[19] The method for producing ultrafine metal particles of the present invention produces ultrafine metal particles by heat-treating a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon in an inert atmosphere. The method is characterized in that the ultrafine metal particles are metal particles whose surface is coated with carbon. The metal oxide preferably contains a transition metal (more preferably, it is composed of a transition metal oxide). The metal particles coated with the generated carbon preferably have an average particle diameter of 1 μm or less.
[0032]
In the production method according to the above [19], more preferably, the powder obtained by mixing the particles containing iron oxide and the particles containing carbon is heat-treated in an inert atmosphere to reduce the iron oxide to at least one of iron and iron carbide. Then, by producing an oxide of carbon, at least one kind of particles of iron or iron carbide, the surface of which is coated with carbon is produced.
[0033]
The method for producing ultrafine metal particles according to the above [19] is characterized in that the step of reducing the metal oxide particles and the step of coating the surfaces of the metal particles with a carbon film are performed in one heat treatment step. The production method of the present invention is superior to the production method of the comparative example described later in that it hardly contains oxygen. The manufacturing method of the comparative example is that, after producing ultrafine metal particles, in order to avoid spontaneous ignition and combustion (oxidation), gradually add oxygen to the ultrafine metal particles in an inert atmosphere containing a low concentration of oxygen. To produce ultrafine particles that form a thin oxide film on the surface.
[0034]
[20] In the above [19], the heat treatment is performed at a temperature of 600 ° C. or more. More desirably, the heat treatment is performed within the range of 600 to 1600 ° C.
[0035]
[21] The method for producing microparticles of the present invention is characterized in that a powder obtained by mixing a powder containing a metal oxide and a powder containing boron is subjected to a heat treatment in an atmosphere containing nitrogen to obtain a fine boron nitride. It is characterized by producing a body. Here, the minute body corresponds to a minute body obtained as a by-product when producing the metal ultrafine particles according to any of the above [1] to [10].
[0036]
[22] {The other method of manufacturing a microscopic object of the present invention is to heat-treat a powder containing boron-containing particles and a metal oxide particle in an atmosphere containing nitrogen to form metal particles or boron nitride. Obtaining a product having at least one of the microparticles. The metal particles may be coated with boron nitride. As the atmosphere containing nitrogen, for example, a nitrogen gas, a mixed gas obtained by mixing a rare gas such as an argon gas with a nitrogen gas, or the like can be used.
[0037]
[23] In the above item [21] or [22], the heat treatment is performed at a temperature of 800 ° C or higher. More preferably, the heat treatment is performed at a temperature in the range of 800C to 1700C.
[0038]
The manufacturing method according to any one of [21] to [23] is extremely excellent in mass productivity. The required thermal energy is small compared to conventional manufacturing methods. Also, high vacuum is not required, and precise pressure control of the atmosphere is not required. Since the inert gas is used, the heat treatment furnace is not damaged, and there is no problem that impurities are mixed into the minute body due to the damage. Moreover, there is no explosive or toxic danger. The oxide powder used as a raw material is easy to produce and handle even if it has nanometer-sized particles. Another advantage is that the raw material is unlikely to be ignited or burned, and the raw material loss or shape due to the ignition or the like is out of design, or the process is not easily interrupted.
[0039]
[24] A powder having fine particles of boron nitride and metal particles is produced by the method for producing fine particles according to any one of [21] to [23], and at least a part of the metal particles is formed from the powder. It is characterized by being removed. It is desirable to remove all of the metal particles to obtain a powder of only boron nitride fine particles. That is, after the heat treatment, a process of removing the metal particles or the minute bodies containing the metal particles is performed. For example, when the metal particles reduced during the heat treatment further grow into coarse metal particles, it is desirable to remove them.
This process is a step for increasing the ratio and purity of boron nitride in the fine powder. For example, by dispersing the microparticles in a medium (liquid) and utilizing the specific gravity difference between metal-based particles and boron nitride microparticles (or the specific gravity difference between metal-containing microparticles and metal-free microparticles), A method of separating and reducing metal particles and the like by a method such as spontaneous sedimentation or centrifugation after stirring can be used (separation method 1). Further, a method of applying a magnetic field to the metal particles to suck the metal particles and separating them from fine particles of only boron nitride that are not sucked (wet or dry method) can be used (separation method 2). Further, a method of reducing the amount of metal particles by chemically dissolving and removing the metal particles with a solution such as an acid can be used (separation method 3). Separation method 3 has the possibility of mixing residual residues and impurities, but is effective in reducing metal particles. In the case where the surface of the metal particles is entirely covered and a solution such as an acid does not penetrate, it is preferable to perform the separation method 1 or the separation method 2 in order to increase the purity of the powdery fine particles. Note that even if metal powder is contained in the fine powder, this is not necessarily a problem. The microparticles are small in size and powder handling is not easy. For example, a powder containing transition metal fine particle powder as a carrier has an advantage that it can be easily handled as compared with a powder composed of only fine particles.
[0040]
[25] The other minute body of the present invention is a minute body produced by reducing a metal oxide in an atmosphere of an inert gas containing nitrogen, and is mainly composed of boron nitride and has a wire shape or It is characterized by being cylindrical. Desirably, boron nitride is a rhombohedral phase. These fine particles are obtained as a by-product when producing the ultrafine metal particles according to the above [1] to [10].
Another minute body of the present invention is a minute body in which nitrogen and boron are combined by reducing a metal oxide in an inert gas atmosphere containing nitrogen, and is mainly composed of boron nitride. It is characterized by a wire shape or a cylindrical shape. By performing a heat treatment in an inert atmosphere containing nitrogen by using a metal oxide as an intermediary or an accelerator, boron and nitrogen are combined to form boron nitride microparticles. As the metal oxide, for example, an oxide of a metal or an alloy can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, an oxide of a magnetic metal is used. For example, the metal or alloy can be selected from Fe, Ni, Co, and alloys containing at least one of them.
[0041]
The term “microscopic object” refers to, for example, a nanotube, a nanowire, a three-dimensional atomic structure, a nanoparticle, a structure having dimensional characteristics on the order of nanometers (nm), an aggregate including at least one of them, or a powder ( Or powder). The microscopic body having a cylindrical shape is more preferably a nanotube. The term “wire or cylinder” refers to, for example, a wire, a rod, a tube, or a tube, which is hollow or solid, any one of which is connected in series, and a small piece (plate-like). (A piece, a scale-shaped or a block-shaped piece).
[0042]
[26] In the above-mentioned [25], the minute body has an average diameter of 0.5 μm or less. Preferably, the average diameter is 0.01 to 0.5 μm, and more preferably, the average diameter is 0.05 to 0.5 μm. More specifically, for example, the diameter can be 0.1 to 0.3 μm.
If a fine powder having an average particle size in the range of 0.001 to 1 μm is used as the raw material metal oxide, a fine body having a diameter in the range of 0.001 to 1 μm can be obtained. More preferably, a metal body having a diameter of 0.001 to 0.05 μm is obtained using a metal oxide having an average particle diameter of 0.001 to 0.05 μm. By using a raw material having a small average particle size and a sharp particle size distribution, fine particles having a small average diameter can be obtained.
[0043]
The diameter corresponds to, for example, the outer diameter of a single microscopic body when a cross section (a cross section in a direction orthogonal to the longitudinal direction) of a wire-like or cylindrical portion is viewed. If the cross section is not circular, the maximum value is regarded as the diameter. When the microscopic body has a diameter that gradually changes along the longitudinal direction, an intermediate value between the maximum diameter and the minimum diameter when viewed in the longitudinal direction may be expressed as the diameter of the microscopic body. If there is a portion that largely deviates from the wire or cylindrical shape, the portion is ignored and the diameter is evaluated only with the wire or cylindrical portion.
[0044]
The average diameter refers to, for example, taking an electron micrograph using a powder having a wire-like or cylindrical fine body as a sample. The diameter of each microscopic object within an arbitrary area in the photograph is measured, and the average value is obtained. That is, the diameter is measured for N microscopic bodies (N ≧ 50), and expressed as average diameter = (sum of measured diameters) / N. Instead of a photograph, an image may be acquired and the diameter measured using a personal computer and image processing software.
[0045]
[27] {The other minute body of the present invention is a cylindrical boron nitride minute body, and has a portion where the ratio of the outer diameter Ro to the inner diameter Ri satisfies (Ri / Ro) ≦ 0.8. Features. When the ratio of Ri / Ro is close to 1, the thickness of the wall becomes small, so that the weight of the minute body becomes small, and as a result, the specific surface area becomes large. The boron nitride microparticles according to the present invention have portions where the ratio of (Ri / Ro) is close to 1, but there are also portions where the inner diameter is small. For example, the inner diameter may be smaller at the end of the cylindrical shape or at a portion where the cylindrical shape is bent, but this is not a problem in practical use.
The boron nitride microparticles can be formed in multiple layers of boron nitride atomic layers constituting the wall of the tube, and can also be generated so as to increase nodes and bridges. Therefore, it is also possible to increase the thickness of the wall of the wire-like or cylindrical minute body to produce a minute body having a small (Ri / Ro). Note that Ri is the inner diameter (corresponding to the diameter of the cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include the cross section of the node. Ro corresponds to the outer diameter of the tube when viewed in a section substantially perpendicular to the longitudinal direction.
[0046]
[28] The other microparticles of the present invention are characterized in that they are a mixture of rhombohedral boron nitride microparticles and hexagonal phase boron nitride microparticles.
With regard to the crystal structure, rhombohedral boron nitride (Rhombohedral @ Boron @ nitride) is also expressed as r-BN. Hexagonal boron nitride (Hexagonal @ Boron @ Nitride) is also represented as h-BN.
[29] The other minute body of the present invention is characterized in that it is boron nitride having a rhombohedral phase and a hexagonal phase.
[0047]
[30] The other minute body of the present invention is mainly composed of boron nitride, is characterized by being cylindrical, and having nodes or bridges inside.
Here, the “node” corresponds to a member that can divide the inside of a cylindrical (or tubular) minute body into a plurality of cavities or divide it into a plurality of sections. “Cross-linking” corresponds to a member that connects arbitrary portions of the inner wall of the cylindrical minute body. It is also possible that the crosslinks are more concentrated to form nodes. The surfaces of the nodes are closely related to the tube wall and the cylindrical wall, rather than being parallel to each other. When there are a plurality of nodes, the interval between the nodes is, for example, 0.5d or more. Here, d corresponds to the diameter d of the cylindrical portion in the middle of the nodes. In addition, even if this micro body has a plurality of nodes, the outer diameter and wall thickness do not always decrease unilaterally, but rather can be increased, so that a long micro body can be obtained. it can.
[0048]
[31] {The other minute body of the present invention is characterized by comprising metal particles, a boron nitride coating covering the metal particles, and wire-shaped or cylindrical boron nitride.
The wire-shaped or cylindrical-shaped portion has not only one growth direction but may have a plurality of growth directions. Further, the wire-shaped or cylindrical boron nitride may be directly grown from a boron nitride film, or may be directly grown from metal particles obtained by reducing a metal oxide. The metal particles may be located at either the tip or the center of the boron nitride microparticles. The arrangement may be a structure in which one metal particle is provided on one boron nitride microparticle (or a structure in which bonding, connection, connection, connection, and connection are provided), or a single metal particle may include a plurality of boron nitride particles. A structure in which elementary bodies are provided is exemplified. As another arrangement state, there is a structure in which metal particles are included in a carbon microparticle (or a structure such as coating, fitting, embedding, inclusion, winding, holding, and carrying). By changing the conditions such as the raw material and the heat treatment in the manufacturing method, the arrangement state of the metal particles can be changed.
The metal particles are preferably made of a transition metal or an alloy containing at least one transition metal. More preferably, the metal particles are made of a magnetic metal. For example, the metal particles have a composition selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0049]
[32] {The other method for producing microscopic particles of the present invention is a method for producing carbon microparticles by subjecting a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon to a heat treatment in an inert atmosphere. Is produced. More desirably, a powder obtained by mixing a powder composed of a transition metal oxide and a carbon powder is heat-treated in an inert atmosphere to produce carbon microparticles. This method for producing a microparticle relates to a microparticle that can be obtained as a by-product when the ultrafine metal particles according to [11] to [20] are produced, and a method for producing the microparticle.
[0050]
[33] {The other method for producing microscopic particles of the present invention is to heat-treat a powder containing carbon-containing particles and metal oxide particles in an inert atmosphere to produce metal particles or carbon microparticles. Obtaining a product having at least one. The metal particles may be coated with carbon.
[0051]
[34] In the above-mentioned [32] or [33], the heat treatment is performed at a temperature of 600 ° C. or more. More desirably, the heat treatment is performed in the range of 600 ° C to 1600 ° C.
[0052]
The manufacturing method according to any one of [32] to [34] is very excellent in mass productivity. The required thermal energy is small compared to conventional manufacturing methods. Further, a high vacuum is not required, and pressure control of the atmosphere and the like are not likely to restrict mass productivity. Since the inert gas is used, there is no damage to the heat treatment furnace, and there is no problem that impurities are mixed into the minute body due to the damage. The oxide powder used as a raw material is easy to produce and handle even if it has nanometer-sized particles. Another advantage is that the raw material is unlikely to be ignited or burned, and the raw material loss or shape due to the ignition or the like is out of design, or the process is not easily interrupted.
[0053]
[35] A powder having carbon microparticles and metal particles is produced by the method for manufacturing microparticles according to any of [32] to [34], and at least a part of the metal particles is removed from the powder. It is characterized by the following. It is desirable to remove all the metal particles to obtain a powder of only carbon fines. That is, after the heat treatment, a process of removing the metal particles or the minute bodies containing the metal particles is performed. For example, when the metal particles reduced during the heat treatment further grow into coarse metal particles, it is desirable to remove them. As this removal process, a process similar to the above [24] can be used.
[0054]
[36] The other minute body of the present invention is a minute body formed by reducing a metal oxide in an inert gas atmosphere, and is made of graphite phase carbon, and has a wire or cylindrical shape. There is a feature. By performing a heat treatment in an inert atmosphere using a metal oxide as a mediator or a promoter, carbon is decomposed and reconstructed to obtain carbon microparticles. These fine particles can be obtained as a by-product when producing the ultrafine metal particles according to [11] to [20].
The microparticles of the present invention are microparticles in which the shape of carbon particles has been reconstructed by reducing a metal oxide in an inert gas atmosphere, and is mainly composed of carbon, and has a wire or cylindrical shape. It is characterized by having. More specifically, a particulate carbon is decomposed and reconstructed by using a reduction reaction for removing oxygen from a metal oxide and an inert gas to generate carbon microparticles. As the metal oxide, for example, an oxide of a metal or an alloy can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, an oxide of a magnetic metal is used. For example, the metal or alloy can be selected from Fe, Ni, Co, and alloys containing at least one of them.
[0055]
[37] In the above-mentioned [36], the minute body has an average diameter of 0.5 μm or less. Preferably, the average diameter is 0.01 to 0.5 μm, and more preferably, the average diameter is 0.05 to 0.5 μm. More specifically, for example, the diameter can be 0.1 to 0.3 μm. If a fine powder having an average particle size in the range of 0.001 to 1 μm is used as the raw material metal oxide, a fine body having an average diameter in the range of 0.001 to 1 μm can be obtained. More preferably, a metal having an average diameter of 0.001 to 0.05 μm is obtained by using a metal oxide having an average particle diameter of 0.001 to 0.05 μm. By using a raw material having a small average particle size and a sharp particle size distribution, fine particles having a small average diameter can be obtained.
[0056]
[38] The other minute body of the present invention is a cylindrical carbon minute body, and has a portion where the ratio of the outer diameter Ro to the inner diameter Ri satisfies (Ri / Ro) ≦ 0.8. I do.
When the ratio of (Ri / Ro) is close to 1, the thickness of the wall becomes small, so that the weight of the minute body becomes small, and as a result, the specific surface area becomes large. The carbon microparticles according to the present invention have portions where the ratio (Ri / Ro) is close to 1, but there are also portions where the inner diameter is small. For example, the inner diameter may be smaller at the end of the cylindrical shape or at a portion where the cylindrical shape is bent, but this is not a problem in practice.
The carbon microparticles can be formed in multiple layers of graphite atomic layers constituting the wall of the tube, and can also be generated so as to increase nodes and crosslinks. Therefore, it is also possible to increase the thickness of the wall of the wire-shaped or cylindrical carbon microparticle to produce a carbon microparticle having a small (Ri / Ro). Note that Ri is the inner diameter (corresponding to the diameter of the cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include the cross section of the node. Ro corresponds to the outer diameter of the tube when viewed in a section substantially perpendicular to the longitudinal direction.
[0057]
[39] The other microscopic body of the present invention is mainly composed of graphite phase carbon, is cylindrical, and has nodes or cross-links therein.
Here, the definition of the “section” is the same as that described in the above [30].
[0058]
[40] The other minute body of the present invention is characterized by comprising metal particles, a carbon coating covering the metal particles, and wire-shaped or cylindrical carbon.
The metal particles are preferably made of a transition metal or an alloy containing at least one transition metal. More preferably, the metal particles are made of a magnetic metal. For example, the metal particles have a composition selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0059]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention according to any of the above [1] to [10] will be described. In the present invention according to the above [1] to [10], the metal powder raw material of the transition metal, in particular, Fe, Co, Ni, etc., serves as a catalyst for boron nitride (BN) formation, When the metal powder and boron (B) were heated at around 2000 ° C., attention was paid to the formation of boron nitride with metal particles as nuclei. Furthermore, when the starting material was not a metal but an oxide of a transition metal represented by Fe, Co, and Ni, the oxide was reduced at 800 ° C. to 1700 ° C., and at the same time, boron nitride was formed. It has been found that new metal ultrafine particles encapsulated in a boron nitride film (BN film) are generated.
[0060]
The concept of the starting materials for metal oxide and boron as the starting materials of the present invention according to the above [1] to [10], the reasons for limiting the numerical values, and the like will be described. As a metal (hereinafter, referred to as M) constituting the oxide according to the present invention, a transition metal or an alloy thereof (particularly, a magnetic material) is preferable. More preferably, Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir or an alloy containing them is suitable. Fe, Co, Ni, Cr, Mn, Mo, Pd, and Ir have a standard enthalpy of formation of an MB bond (B is boron) as H_MB, The standard enthalpy of formation of the MN bond (N is nitrogen) is H_M-N,
H_MB<H_M-N
Is established, and a boride is more easily formed than a nitride. As a result, a metal powder containing boron is formed in the initial stage of the heat treatment, and when nitrogen is present in a gaseous state around the metal powder uniformly, boron and nitrogen contained in the metal powder are finally contained. And it is easy to uniformly coat the surfaces of the metal particles with boron nitride. Metal oxide (M_aO_b) May be a phase diagram conventionally shown, for example, in the case of Fe,₂O₃, Fe₃O₄, FeO.
[0061]
Boron is suitable as a powder of a raw material serving as a boron supply source, but a metal containing boron may be used. As the boron-containing metal (M), the standard enthalpy of formation of the MB bond is H_MB, The standard enthalpy of formation of the MN bond is H_M-N,
H_MB> H_M-N
Is preferable, and Sc, Ti, V, Y, Zr, Nb, La, Hf, and Ta can be mentioned. Compounds having a bond of boron and oxygen in the compound, such as boric acid, are represented by B₂O₃Is not preferable because boron oxide represented by the formula (1) becomes thermodynamically stable and does not become a source of B.
[0062]
(Reaction process)
Fe₂O₃A reaction process in which BN-coated Fe particles, a BN tube, or a BN wire are generated by the reaction between B and B will be described. FIG. 3 schematically shows the reaction process. FIG. 3A shows the state of the raw material. FIG. 3 (2.) Shows an initial stage of the reaction. That is, B is Fe₂O₃Combined with oxygen in the B₂O₃Are generated, and reduced Fe particles are present in the vicinity of B. B₂O₃Is in a liquid or gaseous state. FIG. 3 (3.) shows the further progress of the reaction. At this stage, B reacts with Fe to generate an Fe-B compound. As shown in the figure, the powder structure includes grains of a complete Fe-B compound, grains with incomplete B diffusion to Fe, or grains having a Fe-B compound near the surface with Fe as a core. . When the reaction further proceeds, as shown in FIG. 3 (4.), B in the Fe—B compound reacts with N atoms in the atmosphere, and BN nuclei are generated throughout the particle surface. When these BN nuclei grow, B diffuses from inside the particles to the surface. As a result, only Fe remains inside the particles, and BN-coated Fe particles are generated. When B is excessively present, BN does not only cover Fe, but also expands in a tube or wire shape. FIG. 3 (5.) Is a schematic view of the BN-coated Fe particles and the BN tube.
[0063]
The average particle size of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. If the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and it is not easy to obtain uniform metal particles. The average particle size of the boron powder (b powder) is preferably 0.01 to 100 μm, and more preferably 1 to 50 μm. Boron powder having an average particle size of less than 0.01 μm is expensive and impractical. On the other hand, if the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder will be uneven, and it will be difficult to finally coat the metal particles uniformly. The mixing ratio of the powder a to the powder b is preferably in the range of 25 to 95% by mass of the powder b. If the mass ratio of the b powder is less than 25%, the amount of boron is insufficient and the reduction of the metal oxide is insufficient. If the compounding ratio of the boron powder exceeds 95%, the volume ratio of the reduced metal becomes extremely small, which is not practical.
[0064]
For mixing the a powder and the b powder, a V-type mixer, a crusher (for example, a device that combines crushing and mixing like a raikai machine), a mortar, and the like are used. A predetermined amount of the mixed powder is filled in a heat-resistant crucible made of alumina, boron nitride, or the like, and heated under predetermined conditions. The atmosphere during the heat treatment is preferably a nitrogen gas atmosphere, an ammonia gas atmosphere, or a mixed gas atmosphere containing them. The mixed gas may be mixed with an inert gas such as argon or helium. Gases containing oxygen, such as air, are not suitable because they hinder the reduction reaction. The heat treatment temperature is preferably from 800C to 1700C, more preferably from 1000C to 1400C. If the temperature is lower than 1000 ° C., the time required for completing the reaction becomes longer. If the temperature is lower than 800 ° C., the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in a non-oxygen atmosphere, oxygen may be released due to the decomposition of the oxide ceramic used as a furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. If the temperature exceeds 1700 ° C., the use of heat-resistant members is indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
[0065]
Next, an embodiment of the present invention according to any one of the above [11] to [20] will be described. According to the present invention relating to the above [11] to [20], a transition metal oxide represented by Fe, Co, and Ni is selected as a raw material of a transition metal metal powder, and heated to 600 ° C. to 1600. It was found that the oxides were reduced at ℃ and that carbon mainly composed of graphite was formed on the surface of the metal particles. In addition, the inventors have found a configuration in which metal particles are included in a carbon coating. It is considered that transition metals, particularly Fe, Co, and Ni, which are constituent elements of the starting material, play a role of a catalyst for forming a graphite layer.
[0066]
As a powder of a raw material serving as a carbon supply source, carbon powder such as graphite, carbon black, and natural graphite is suitable, but a compound containing carbon may be used. That is, coal, activated carbon, coke, fatty acids, polymers such as polyvinyl alcohol, BC compounds, and carbides containing metals may be used. Therefore, in the claims and the means for solving the problems, the term "carbon powder" is used as a term including both carbon powder and compounds containing carbon. However, in order to increase the carbon purity of the coating, carbon powder is preferably used.
[0067]
The average particle size of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. If the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and it is not easy to obtain uniform metal particles. The average particle size of the carbon powder (b powder) is preferably from 0.01 to 100 μm, more preferably from 0.1 to 50 μm. Carbon powder having an average particle size of less than 0.1 μm is expensive and impractical. On the other hand, if the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder will be uneven, and it will not be possible to finally coat the metal particles uniformly. The mixing ratio of the powder a to the powder b is preferably in the range of 25 to 95% by weight of the powder b. When the weight ratio of the b powder is less than 25%, the reduction reaction does not sufficiently proceed due to insufficient carbon. On the other hand, if the mixing ratio of the powder b exceeds 95%, the volume ratio of the reduced metal becomes extremely small, which is not practical. Making the average particle diameter in the range of 0.001 to 1 μm, more desirably in the range of 0.01 μm to 0.1 μm is necessary for applying the metal ultrafine particles of the present invention to a magnetic recording medium, a magnetic shield, an electronic device and the like. desirable.
[0068]
For mixing the a powder and the b powder, a V-type mixer, a crusher (for example, a device that combines crushing and mixing like a raikai machine), a mortar, and the like are used. The mixed powder is heat-treated under a predetermined condition by filling a predetermined amount of a transition metal oxide and a carbon compound into a heat-resistant crucible such as alumina, boron nitride, and graphite. The atmosphere during the heat treatment is not limited as long as it is an inert gas, but a mixed atmosphere of an inert gas such as a nitrogen gas or an argon gas containing nitrogen as a main component can be used. The heat treatment temperature is preferably from 600C to 1600C, more preferably from 900C to 1400C. If the temperature is lower than 900 ° C., the time required for completing the reaction becomes long. If the temperature is lower than 600 ° C., the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in a non-oxygen atmosphere, oxygen may be released due to decomposition of the oxide ceramic used as a furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. If the temperature exceeds 1600 ° C., the use of heat-resistant members is indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
[0069]
Next, embodiments of the invention relating to the above [21] to [31] will be described.
According to the present invention according to the above [21] to [31], when the oxide (a powder) of a transition metal and the boron powder (b powder) are heated at a temperature of 800 to 1700 ° C. in a nitrogen atmosphere, the metal oxide The material serves as a catalyst for boron nitride microparticle formation, and can produce wire-shaped boron nitride microparticle powder having an average diameter of 0.5 μm or less. It is possible to produce boron nitride microparticles at a lower temperature than in the prior art.
[0070]
As the metal constituting the oxide of the a powder, a transition metal or an alloy thereof (especially a magnetic material) is preferable, and more preferably, Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir or an alloy containing them is suitable. I have. Metal oxide (M_aO_b) May be those conventionally shown in a phase diagram. For example, when M is Fe, Fe₂O₃, Fe₃O₄, FeO. The metal oxide is reduced in the process of forming boron nitride, and eventually becomes metal particles.
[0071]
Further, the b powder may be a metal powder containing boron in addition to the boron powder. As the boron-containing metal (M), the standard enthalpy of formation of the MB bond (B is boron) is H_MB, The standard enthalpy of formation of the MN bond (N is nitrogen) is H_M-N,
H_MB> H_M-N
It is preferable that the relationship is established. Specifically, Sc, Ti, V, Y, Zr, Nb, La, Hf, and Ta are mentioned.
[0072]
The average particle size of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. On the other hand, if the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and does not function sufficiently as a catalyst. The average particle size of the boron powder (b powder) is preferably 0.01 to 100 μm. Boron powder having an average particle size of less than 0.01 μm is expensive and impractical. On the other hand, if the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder becomes uneven, and it becomes difficult to finally coat the metal particles uniformly. The mixing ratio of the powder a to the powder b is preferably in the range of 25 to 95% by weight of the powder b. If the weight ratio of the b powder is less than 25%, boron will be insufficient and the formation of boron nitride will be insufficient. On the other hand, if the mixing ratio of the powder b exceeds 95%, the amount of the powder a decreases and the catalytic function deteriorates, and the formation of boron nitride becomes insufficient.
[0073]
A V-type mixer, a mortar, or the like is used for mixing the powder a and powder b. A predetermined amount of the mixed powder is filled in a heat-resistant crucible such as alumina or boron nitride and heat-treated under predetermined conditions. The atmosphere during the heat treatment is preferably a nitrogen gas atmosphere or a mixed gas atmosphere containing nitrogen gas. The mixed gas may be mixed with an inert gas such as Ar or He. Gases containing oxygen, such as air, are not suitable. The heat treatment temperature is preferably from 800C to 1700C, more preferably from 1000C to 1400C. If the temperature is lower than 1000 ° C., the time required for completing the reaction becomes longer. If the temperature is lower than 800 ° C., the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in an inert gas atmosphere, oxygen may be released due to decomposition of the oxide ceramic used as a furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. . If the temperature exceeds 1700 ° C., the use of heat-resistant members is indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
[0074]
The crystal structure of the boron nitride powder obtained by the above method is identified by X-ray diffraction measurement. As shown in FIG. 18, hexagonal boron nitride (h-BN) and rhombohedral boron nitride (r-BN) are obtained. Can be detected. FIG. 18 shows the results obtained by measuring the powder obtained in Example 7 described later. Further, when the powder structure was observed by TEM observation, it was confirmed that wire-like boron nitride was formed as shown in FIG. 19, and it was identified as h-BN from the observation of the lattice image.
[0075]
Next, embodiments of the invention relating to the above [32] to [40] will be described. According to the present invention according to the above [32] to [40], when the transition metal oxide (a powder) and the carbon powder (b powder) are heated at a temperature of 600 to 1600 ° C. in an inert gas atmosphere, the metal The oxide serves as a catalyst for forming carbon microparticles, and can produce wire-shaped carbon microparticle powder having an average diameter of 0.5 μm or less.
[0076]
Transition metals or alloys thereof (particularly magnetic materials) are preferable as the metal constituting the oxide of the powder a. Metal oxide (M_aO_b) May be those conventionally shown in a phase diagram. For example, when M is Fe, Fe₂O₃, Fe₃O₄, FeO. The metal oxide is reduced in the course of carbon formation, and eventually becomes metal particles.
[0077]
As the b powder, carbon powder such as graphite, carbon black, and natural graphite is suitable, but a compound containing carbon may be used. That is, coal, activated carbon, coke, fatty acids, polymers such as polyvinyl alcohol, BC compounds, and metal carbides may be used.
[0078]
The average particle size of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. On the other hand, if the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and does not function sufficiently as a catalyst. The average particle size of the carbon powder (b powder) is preferably 0.01 to 100 μm. Carbon powder having an average particle size of less than 0.01 μm is expensive and not practical. The mixing ratio of the powder a to the powder b is preferably in the range of 25 to 95% by weight of the powder b. If the weight ratio of the b powder is less than 25%, carbon is insufficient. On the other hand, when the blending ratio of the b powder exceeds 95%, the amount of the a powder decreases and the catalytic function decreases.
[0079]
A V-type mixer, a mortar, or the like is used for mixing the powder a and powder b. A predetermined amount of the mixed powder is filled in a heat-resistant crucible such as alumina or boron nitride and heat-treated under predetermined conditions. The atmosphere during the heat treatment is preferably in an inert gas atmosphere. Gases containing oxygen, such as air, are not suitable. The heat treatment temperature is preferably from 600C to 1600C, more preferably from 900C to 1400C. If the temperature is lower than 900 ° C., the time required for completing the reaction becomes long. If the temperature is lower than 600 ° C., the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in an inert gas atmosphere, oxygen may be released due to decomposition of the oxide ceramic used as a furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. . If the temperature exceeds 1600 ° C., the use of heat-resistant members is indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
[0080]
【Example】
Hereinafter, the present invention will be described with reference to examples. However, the present invention is not necessarily limited by these examples.
(Example 1)
Α-Fe with an average particle size of 0.6 μm₂O₃5 g of powder (a powder) and 5 g of boron powder (b powder) having an average particle size of 30 μm were weighed, and each powder was put into a V-type mixer so that the mixing ratio of b powder was 50% by mass. And mixed for 10 minutes. An appropriate amount of the mixed powder was filled in an alumina boat, placed in a furnace, and heated at a rate of 3 ° C./min from room temperature in a nitrogen gas stream having a flow rate of 2 (l / min). For 2 hours and cooled in the furnace to room temperature. The mixed powder before the heat treatment was red-black, but the powder after the heat treatment turned grayish white. When X-ray diffraction measurement (Cu, Kα ray) was performed on each of the powders before and after the heat treatment, diffraction patterns as shown in FIG. 1 (before heat treatment) and FIG. 2 (after heat treatment) were obtained. From the heat-treated powder, a (002) peak of hexagonal boron nitride (h-BN) and a (110) peak of α-Fe were mainly detected. The Fe particle diameter calculated from the (110) peak of Fe using the analysis software “Jade5” manufactured by Rigaku was 89 nm. Table 1 summarizes the particle diameter of each phase and Fe detected from the X-ray diffraction pattern. Table 2 shows the results of measuring the magnetic properties of this off-white powder using a VSM. The saturation magnetization is at least 20 times the value of Comparative Example 2 to be described later.₂O₃Is reduced to Fe. Further, only the powder sucked up by a permanent magnet from this grayish white powder was subjected to a corrosion resistance test at 100% humidity and 120 ° C. for 24 hours using a PCT tester, and then subjected to oxygen analysis by an incineration method. Table 3 shows the obtained results.
[0081]
(Example 2)
Fe₂O₃Fe instead of powder₃O₄An off-white powder was prepared in the same manner as in Example 1 except that powder (average particle size: 0.5 μm) was used, and was subjected to X-ray diffraction, VSM measurement, and PCT test.
[0082]
(Comparative Example 1)
The mixed powder was heat-treated and subjected to X-ray diffraction and VSM measurement in the same manner as in Example 1 except that the mixing ratio of the boron powder (b powder) was changed to 20% by mass ratio.
(Comparative Example 2)
The mixed powder was subjected to heat treatment in the same manner as in Example 1 except that the heat treatment temperature was changed to 500 ° C., and X-ray diffraction and VSM measurement were performed.
(Comparative Example 3)
A corrosion resistance test was performed on Fe powder having an average particle diameter of 20 nm (ultrafine particles manufactured by Vacuum Metallurgy Co., Ltd.) under the same conditions as in Example 1. Table 3 shows the results.
[0083]
[Table 1]

[0084]
[Table 2]

[0085]
[Table 3]

[0086]
(Example 3)
5 g of Ni-containing Fe oxide powder and 5 g of boron powder were charged into a V-type mixer and mixed. An appropriate amount of the mixed powder was filled in an alumina boat, placed in a furnace, and heated at a rate of 3 ° C./min from room temperature in a nitrogen gas stream having a flow rate of 2 (l / min). For 2 hours and cooled in the furnace to room temperature. Observation of the powder after the heat treatment revealed metal particles whose surfaces were coated with boron nitride. Composition analysis revealed that the metal particles were Fe containing Ni.
[0087]
(Example 4)
The operation of separating metal particles and BN or C will be described. FIG. 4 shows a manufacturing process diagram of the BN-coated metal particles and the BN fine particles. When manufacturing coated metal particles, the manufacturing process is as follows: S1 → S2 → S3 → S4 in FIG. In S2, the crucible made of boron nitride containing the raw material powder was heat-treated in a tubular furnace 43. Since the heat-treated powder obtained in S2 was the mixed powder 41 of the coated metal particles and the fine particles, the coated metal particles were recovered through the steps of separation and purification of S3 and S4. In the step S3, the heat-treated powder dispersed in a medium 45 typified by an organic solvent such as acetone or ethanol was stirred in the washing tank 44 to spontaneously settle the coated metal particles. As a means for stirring, an ultrasonic cleaning device 46 was used to apply ultrasonic waves to the cleaning tank 44. In addition, when stirring was performed by using a stirrer such as a manual stirrer using a glass rod or a pencil mixer instead of the application of ultrasonic waves, sufficient stirring was achieved.
[0088]
In step S4, the supernatant 47 was removed and the precipitate was dried to collect the coated metal particles 48. At the same time, when the supernatant was dried, BN microparticles were recovered. In the above process, BN-coated metal particles and BN fine particles could be obtained at the same time. In particular, when only the BN minute body is manufactured, the manufacturing process may be S1 → S2 → S5 → S6 in FIG. Step S5 is a step of dissolving the metal particles in the heat-treated powder with an acidic solution such as hydrochloric acid or sulfuric acid. After immersing the heat-treated powder in the acidic solution, the precipitate was recovered. Step S6 is a step of washing the precipitate with water and then drying it. An appropriate amount of pure water was poured into the precipitate obtained in S5, and the mixture was stirred with a glass rod or the like, and then precipitated again to remove a supernatant, followed by drying to obtain BN microparticles. For complete removal of the acidic solution, step S6 is preferably repeated several times. In addition, the said manufacturing process was applicable also to the process of manufacturing the metal particle and carbon microparticle covered with carbon.
[0089]
FIG. 5 is a micrograph of the particle structure according to the present invention observed with an electron microscope (TEM), and shows BN-coated Fe particles. FIG. 6 is a schematic diagram for schematically explaining the structure of FIG. As shown in FIG. 6, the periphery of the Fe particle 1 is covered with a BN film 2. FIG. 7 shows a further enlarged photograph of the state of the BN film.
[0090]
FIG. 7 is a micrograph of the particle structure according to the present invention observed with an electron microscope, and shows Fe particles coated with BN. FIG. 8 is a schematic diagram for schematically explaining the structure of FIG. As shown in FIG. 7, in the BN film coated on the surface of the Fe particles 1, a stripe pattern of the laminated crystal lattice is observed. In the part of the lattice plane 3, a plurality of lattice planes are stacked substantially in parallel with each other along the surface of the Fe particle 1. It can be seen that the lattice planes 4 and 5 have portions where the lattice planes are not parallel to each other, but sufficiently cover the surface of the Fe particles 1.
[0091]
(Example 5)
Α-Fe with an average particle size of 0.03 μm₂O₃5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle size of 20 μm were charged into a V-type mixer and mixed for 10 minutes. This mixed powder 51 is filled in an appropriate amount into a crucible 52 made of boron nitride, and the crucible 52 is set in a tubular furnace 53 and heated at a rate of 3 ° C./min from room temperature in a nitrogen gas flow at a flow rate of 2 l / min. After that, it was kept at 1000 ° C. for 2 hours and cooled in a furnace at a rate of 3 ° C./min to room temperature. The structure of the tube furnace is shown schematically in FIG. When X-ray diffraction measurement (Cu, Kα ray) was performed on each of the powders before and after the heat treatment, diffraction patterns as shown in FIG. 9 (before heat treatment) and FIG. 10 (after heat treatment) were obtained. From the powder subjected to the heat treatment, a (002) peak of graphite and a (110) peak of α-Fe were mainly detected. Table 4 shows the results of measuring the magnetic properties of the powder after the heat treatment with a VSM (Sample Vibration Magnetometer). The saturation magnetization is about 100 times the value of Comparative Example 4, and together with the result of the X-ray diffraction measurement,₂O₃Is reduced to Fe. After exposing the powder after the heat treatment with a PCT tester (pressure cooker test tester) at 100% humidity, 120 ° C. and 1 atm for 24 hours, the oxygen content of the powder is measured by an oxygen / nitrogen / hydrogen analyzer in metal ( The analysis was performed using a Horiba EMGA-1300). Table 5 shows the analysis results of the oxygen content. After the PCT test, there was no increase in the amount of oxygen, confirming that the surface of the Fe powder was covered with the graphite film. In the analysis of oxygen, nitrogen and hydrogen in the metal, O, N and H in the sample were thermally decomposed by filling a graphite crucible with 0.5 g of sample powder and rapidly heating the crucible to 2000 to 3000 ° C. Gas generated by gas chromatograph and thermal conductivity detector₂, N₂, H₂This is a method of analyzing the contents of O, N, and H by detecting O gas.
[0092]
(Comparative Example 4)
The mixed powder was heat-treated and subjected to X-ray diffraction, VSM measurement and PCT test in the same manner as in Example 5 except that the heat treatment temperature was changed to 500 ° C. The X-ray diffraction pattern did not change before and after the heat treatment, and the reaction did not proceed. The value of the saturation magnetization hardly changes.
[0093]
(Comparative Example 5)
A corrosion resistance test was performed on Fe powder (ultrafine particles manufactured by Vacuum Metallurgy Co., Ltd.) having an average particle size of 0.02 μm under the same conditions as in Example 5. The saturation magnetization is the value of pure iron (about 260 × 10^-6wb · m / kg) to about 30%.
[0094]
[Table 4]

[0095]
[Table 5]

[0096]
FIG. 11 is a photomicrograph of the structure of the ultrafine metal particles according to Example 5 observed with a TEM (transmission electron microscope). In the TEM observation, no processing for causing damage or mutation to the particles was performed except for the necessary sample preparation. FIG. 12 is a schematic diagram schematically illustrating the structure of FIG. 11 and is slightly enlarged. The metal ultrafine particles 11 are particles in which the surfaces of the α-Fe particles 12 are all coated with a graphite thin film 20 having a predetermined thickness. This coating protects the surface of the α-Fe particles 12 and effectively prevents oxidation. The projections 21 and 21b scattered outside the graphite thin film 20 are presumed to be either a growth of a different layer of graphite or a deposition of foreign matter. The light-dark patterns 13a, 13b, 13c of the α-Fe particles 11 themselves are interference patterns (indicated by two-dot chain lines) resulting from the shape (substantially spherical) of the α-Fe particles 11. At both ends of the α-Fe particle, the boundary 14 of the graphite thin film is photographed slightly indistinctly, and therefore is indicated by a dotted line. This is because it is difficult to focus on everything due to the substantially spherical shape, and the actual shape is not unclear. The region indicated by the dashed line is the collodion film 15 for fixing the metal ultrafine particles 11 to the sample holder for TEM observation. The line and reference numeral 16 are on a scale whose three lines have a length of 20 nm. The scale at the time of photographing FIG. 11 was copied and added to FIG.
[0097]
FIG. 13 is a photomicrograph of the particle structure according to the present invention observed with a TEM (transmission electron microscope), and illustrates the state of the graphite thin film 20 by enlarging the lower left half of FIG. The structure of FIG. 13 will be schematically described with reference to the schematic diagram of FIG. The graphite thin film 20 mainly has a crystal structure of graphite. For example, the lattice fringes 20a, 20b, and 20c represent layered lattice planes of graphite, and the lattice fringes have substantially equal intervals, and are arranged substantially parallel to the surface of the α-Fe particles 12.
[0098]
However, since the α-Fe particles are spherical and have some irregularities on the surface, a part of the graphite thin film is inclined with respect to the surface of the α-Fe particles 12 like lattice fringes 20f. In some places. The lattice fringe 20f is derived from another lattice fringe 20e, and further has a lattice fringe 20d. Although the lines are not shown, the lattice fringes 20d are arranged substantially parallel to the surface of the α-Fe particles 12. As described above, in the graphite thin film, there is a portion where the orientation of the layered lattice plane changes or the arrangement state becomes unclear (a portion which looks like a satin pattern). In addition, since the crystal structure is grown so that the plane of the crystal structure becomes parallel to the surface of the α-Fe particle 12, a substantially uniform coating of the graphite thin film is formed.
[0099]
In the graphite thin film 20 of FIG. 14, a part of the lattice fringe is schematically illustrated by a solid line or a dotted line. Although not shown, a crystal structure also exists in a blank portion. In addition, it is presumed that an intermediate layer 25 exists between the surface of the α-Fe particles 12 and the graphite thin film 20, and details thereof will be described with reference to FIGS.
[0100]
FIG. 15 is a micrograph of the structure of the particles according to the present invention observed by a TEM (transmission electron microscope), and is a further enlarged photograph of the vicinity of the graphite thin film 20 of FIG. FIG. 16 is a schematic diagram schematically illustrating the structure of FIG. 15 and is slightly enlarged. In the α-Fe particles 12, lattice fringes 24 are observed along the direction of the arrow a, indicating a unique crystal plane of α-Fe. Since it is difficult to precisely reproduce the arrangement of Fe atoms in a daisy chain, they are indicated by dotted lines. In the vicinity of the surface of the α-Fe particle 12, the lattice fringe along the arrow a is broken, but the end of the array forms a flat surface, and the starting point for the graphite crystal to grow gradually. (Graphite growth layer). Hereinafter, these regions are referred to as an intermediate layer 25. The graphite thin film 20 is grown and formed via the intermediate layer 25.
[0101]
As shown in FIG. 16, if the surface of the α-Fe particles 12 is a relatively smooth spherical surface (flat surface), the graphite layered lattice surface 22 becomes a surface along the arrow d, and is regularly arranged in parallel. As it grows, it forms a dense and very thin coating. Here, “dense” refers to having a portion where regular lattice planes are stacked. In the direction perpendicular to the arrow d, 15 to 17 layers of the layered lattice were laminated to form a very thin film. The thickness of the intermediate layer 25 looks like one or two layers in terms of the interval between the graphite layered lattice planes 22. When the crystal plane of graphite that has started to grow is also included in the intermediate layer, the thickness of the intermediate layer 15 is about 2 to 4 layers in terms of the interval between the layered lattice planes 22 of graphite.
[0102]
The dislocation 23 is presumed to be a portion where the crystal growth is shifted and the crystal structure is discontinuous. It is assumed that when a layered lattice grows to have a laminated structure, the growth of a certain portion is delayed by one layer due to a lattice defect. When the growth of a certain part is restarted, the lattice plane of the (n-1) th layer in a certain part and the lattice plane of the nth layer in an adjacent part may combine to form one plane (dislocated plane). . The occurrence rate of dislocation planes is not high, and it can be said that the entire coating is a uniform and dense thin film. Although the projections 21b exist on the surface of the graphite thin film 20, they were not clearly photographed in the photograph of FIG.
[0103]
(Example 6)
Hematite having an average particle size of 0.03 μm (Fe₂O₃3) 3 g of powder and 7 g of boron powder having an average particle size of 26 μm were charged into a V-type mixer and mixed for 10 minutes. The mixed powder 121 is filled in a crucible 122 made of boron nitride, placed in a tubular electric furnace 123, and heated from room temperature at a rate of 3 (° C./min) in a nitrogen gas flow at a flow rate of 2 (l / min). After heating, the mixture was kept at 1100 ° C. for 2 hours and cooled in a furnace to room temperature. The mixed powder before the heat treatment was red-black, but the powder after the heat treatment turned grayish white. X-ray diffraction measurement (Cu, Kα ray) of the heat-treated powder gave a diffraction pattern as shown in FIG. 17. From the heat-treated powder, hexagonal boron nitride (h-BN) was obtained. ), Rhombohedral boron nitride (r-BN) and α-Fe diffraction peaks were detected. To separate boron nitride and Fe, 500 cc of acetone (0.5 × 10^-3m³) Was charged with 5 g of the above powder and subjected to ultrasonic cleaning for 5 minutes to separate a supernatant and a precipitate. The supernatant 127 was left in the fume hood for further 24 hours to dry the acetone, and a boron nitride powder 128 (weight 6 g) was recovered.
[0104]
When this boron nitride powder was observed with a transmission electron microscope (TEM), a wire-like structure as shown in the photograph of FIG. 19 was observed. When the lattice image was analyzed, the boron nitride wire had a rhombohedral structure. The unit of flow rate is (l / min) ≒ about 16.7 × 10^-6(M³/ S). The manufacturing process of Example 6 includes a powder mixing process (S11), an atmosphere heat treatment process (S12), an ultrasonic application process to a medium in which the powder is dispersed (S13), and a separation and drying process of the boron nitride microparticles ( S14) and corresponds to the process flow and schematic diagram of FIG. In the figure, reference numeral 124 denotes a cleaning tank, reference numeral 126 denotes a supersonic cleaning machine, and reference numeral 125 denotes a solvent (acetone) in which the powder after heat treatment is dispersed. In addition, as long as an ultrasonic wave can be applied in order to disperse the generated particles, it can be used without being limited to a washing machine.
[0105]
FIG. 20 is a schematic view which replicates the structure of the photograph of FIG. 19 and shows a wire-like boron nitride microparticle. The boron nitride minute body 101 has a long bent tube shape formed by connecting a plurality of tubes 103 each having a cavity 102 therein. One end is terminated by the structure of the tube 103. The other end is terminated with the h-BN tissue 112 via a tissue in which the r-BN tissue as the tube 103 and the h-BN-like portion 112b are mixed. In FIG. 20, the curve indicated by the dotted line represents the extension of the collodion film for fixing the boron nitride microparticles 101 to the sample holder of the electron microscope. The lines and letters outside the right of the rectangular box in FIG. 20 indicate that the line length corresponds to a dimension of 200 nm.
[0106]
FIG. 21 is a schematic diagram in which only the boron nitride tube in FIG. 20 is extracted and enlarged. The vicinity 111 of the distal end of the tube is seen overlapping with the middle part of the tube, and it is not clear whether the distal end is closed because it is not clear. From the vicinity of the tip, the structure of the cavity 102 and the tube 103 surrounding the cavity 102 continues. On the way, a portion considered to be a node 104 between the tubes and a portion where the tube is thick or looks thick for oblique observation. There are possible bumps 105. The direction of the continuous tube appears to be greatly bent at the bending portion 110, for example. The thickness of the tube does not always look uniform and forms the cavity 102 with not only the bumps 105 and nodes, but also a complex line or striae-like structure. The tube structure is clearly observed from near the tip 111 to the node 104b, and the diameter of the tube is 0.12 to 0.20 μm (120 to 200 nm). In this area, since the crystal structure is complicated, it is presumed that r-BN and h-BN are mixed or a mixed phase is formed. It is considered that the mixture of different phases is related to the bending of the tube. When the crystal structure of the tube 103, which looks clearly like a pipe, is magnified and observed, the arrangement of atoms is r-BN that repeats a three-layer cycle, and the direction of the cycle is oriented in the diameter direction of the tube.
[0107]
(Example 7)
Α-Fe with an average particle size of 0.03 μm₂O₃5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle size of 20 μm were charged into a V-type mixer and mixed for 10 minutes. This mixed powder 251 is charged into a boron nitride crucible 252 in an appropriate amount, and the temperature is raised from room temperature at a rate of 3 ° C./min in a tubular furnace 253 at a flow rate of 2 ° C./min. The furnace was cooled to a room temperature at a rate of 3 ° C./min. The unit of flow rate is (l / min) ≒ about 16.7 × 10^-6(M³/ S).
[0108]
X-ray diffraction measurement (Cu, Kα ray) of each powder before and after the heat treatment resulted in diffraction patterns as shown in FIG. 23 (before heat treatment) and FIG. 24 (after heat treatment). From the powder subjected to the heat treatment, a (002) peak of graphite and a (110) peak of α-Fe were mainly detected. In FIG. 24, the mark ○ indicates a peak corresponding to the crystal structure of graphite, the mark ■ indicates a peak corresponding to the crystal structure of α-Fe, the horizontal axis indicates the diffraction angle 2θ (°), and the vertical axis indicates the diffraction angle. X-ray intensity (cps). The maximum intensity peak of graphite has a half width of about 0.2 °, and the crystallinity of the powder after heat treatment is good. Further, when the magnetic properties of the powder before and after the heat treatment corresponding to FIGS. 23 and 24 were measured by a VSM (sample vibration magnetometer), the saturation magnetization was 1.30 × 10^-6Wb · m / kg, 131 × 10 for the latter^-6Wb · m / kg. From the above, Fe₂O₃Is reduced to Fe.
[0109]
When the powder after the heat treatment was observed by a TEM (transmission electron microscope), a tube-shaped microscopic body as shown in FIG. 25 was confirmed. FIG. 25 is a micrograph of the particle structure according to the present invention observed with an electron microscope. As a result of a composition analysis by EDX (energy dispersive X-ray detector), it was found that the black particles at the tip of the minute body were Fe and the tube was C (carbon).
[0110]
FIG. 26 is a schematic diagram corresponding to the structure of the photograph of FIG. The carbon minute body 201 has a structure in which a carbon tube 203 is grown in a curved shape based on the Fe particles 202. A plurality of nodes 204 are present inside the tube 203, and the region surrounded by the opposing nodes and the tube wall 203 b forms a cavity 205. The other end of the tube 203 is closed, forming a tip 206. In the carbon microparticles 201, it is considered that the bent growth direction of the tube is related to the fact that the wall thickness of the tube and the interval between nodes are not uniform. In particular, the portions of the tube walls 203c and 203e are thin.
[0111]
Another carbon microparticle 207 has a structure in which a carbon tube 209 grows in a curved shape based on the Fe particle 208 and includes another Fe particle 213 at the tip. A plurality of nodes 210 are present inside the tube 209, and the area surrounded by the opposing nodes and the tube wall forms a cavity 211. The Fe particles 220 near the Fe particles 213 appear to be separated by the tube wall 220 or the like. In the carbon microparticles 207, it is not clear whether the Fe particles 213 were attached from the beginning of the growth of the tube or were taken in during the growth of the tube. Note that the Fe particles 208 and the wall 212 of the tube are only seen overlapping with the carbon microparticles 201 and are not connected. Further, other Fe particles 214 exist alone. In the figure, a straight or bent dashed line represents the contour of the raw material carbons 215 and 216. The curved dashed-dotted lines indicate the contours of the collodion films 217 and 218 for fixing the carbon microscopic bodies and the like to the sample holder of the electron microscope. Reference numeral 219 denotes a scale display entered for easy understanding of the dimensions in FIG. 26, and the original FIG. 25 does not have such a structure. The length of the three lines in the scale display corresponds to 100 nm.
[0112]
Based on the photograph of FIG. 25, the ratio of the outer diameter Ro to the inner diameter Ri of each carbon microparticle was measured. Measurement is performed at an arbitrary position to obtain data such as (Ri / Ro) = 0.67, 0.75, 0.40, 0.69, 0.57, 0.63, 0.75, 0.44. Was. When the carbon microparticles were manufactured by changing the conditions of Example 8, the average outer diameter and the average inner diameter could be changed. In consideration of these condition changes, the upper limit of (Ri / Ro) can be set to 0.8.
[0113]
FIG. 27 is a micrograph of the particle structure according to the present invention observed with an electron microscope. In FIG. 25, the vicinity of the joint between the Fe particle 202 and the tube 203 is enlarged. FIG. 28 is a schematic diagram corresponding to the structure of the photograph of FIG. In FIG. 28, for the sake of simplicity, only the main part of the crystal structure of FIG. 27 is represented by solid lines and dotted lines. Therefore, even if the area around the area hatched by the dotted line is blank, only that part is omitted.
[0114]
According to FIG. 28, the Fe particles 202 had a structure that appeared to have a surface along a specific crystal plane in most regions. Hereinafter, these are referred to as Fe main phases 220 and 221. On the left side of the Fe main phase 220, a phase 225 having a different orientation of the arranged surface and a hetero phase 226 that looks like a satin pattern were observed. In addition, although the Fe main phase 220 and the like are represented by dotted lines arranged in parallel, the point intervals and the line intervals do not always match those in FIG. It is drawn for easy understanding of the direction of the line arrangement and the like.
[0115]
The carbon tube in FIG. 28 will be described. The tube 203 is formed ahead of the virtual boundary line 227 and the Fe main phase 221. It can be seen that the inside of the wall of the cylindrical tube is a structure partitioned by nodes 236 and 239. The region surrounded by the node 236 and the Fe particles 202 and the tube wall, or the region surrounded by the nodes 236 and 239 and the tube wall became hollow.
[0116]
The wall of the tube is mainly composed of a phase in which the crystal arrangement is a graphite structure. Hereinafter, graphite and a structure similar thereto are collectively referred to as a graphite phase. The graphite phase is more distinct than Fe in that the crystal arrangement appears to be stacked along a particular plane. The surfaces of the graphite phases 230, 231, 232, 233, 237, 238, 240 can be said to be parallel or substantially parallel to the growth direction of the tube wall. On the other hand, in the nodes 236 and 239, the surface of the graphite layer can be said to be orthogonal or substantially orthogonal to the growth direction of the tube wall. At the left base of the node 236, the direction of the graphite layer is divided in a Y-shape into a downward layer 234 and an upward layer 235, and has a structure like a tree trunk and a branch. The root of node 239 is substantially perpendicular to the wall of the tube, and it is believed that there are at least two types of node tissue. The graphite phase 242 is considered to be a crosslink or a node, but cannot be concluded because the graphite phase 242 of another structure is intermingled.
In addition, in the state of lamination of the atomic arrangement of the graphite layers, the intervals are narrow as expressed in the graphite layers 235 and 238 and the nodes 236 and 239. If all the layers are similarly illustrated, the drawing becomes complicated. Therefore, in other portions, the number of layers is reduced and illustrated. In addition, when one layer can be clearly understood, it is shown by a line. However, when it seems that the layer is continuous, it is shown by a dotted line.
[0117]
5 g of the heat-treated powder was put into 500 cc of acetone and subjected to ultrasonic cleaning for 5 minutes to separate a supernatant and a precipitate. The supernatant 257 was left in the fume hood for a further 24 hours to dry the acetone, and a carbon fine powder 258 was obtained. The powder 258 has an improved ratio of carbon microparticles by removing coarse transition metal particles and the like.
[0118]
The manufacturing process of Example 7 includes a powder mixing process, a heat treatment process in an atmosphere, an ultrasonic wave application (dispersion process) to a medium into which the powder is charged, a separation process of coarse transition metal particles and the like, and a drying process. Corresponds to the flow and schematic diagram. In the figure, reference numeral 254 denotes a cleaning tank, reference numeral 255 denotes a solvent (acetone) in which the powder after heat treatment is dispersed, and reference numeral 256 corresponds to an ultrasonic cleaning device. In addition, as long as ultrasonic waves can be applied to disperse the generated particles in a solvent, the particles can be used without being limited to the cleaning device.
[0119]
【The invention's effect】
As described above, by using the metal ultrafine particles of the present invention and the method for producing the same, it is possible to obtain metal ultrafine particles in which a coating suitable for industrial use is provided on a metal particle surface in a safe and simple manner. Furthermore, when manufacturing ultrafine metal particles, it is possible to obtain fine particles related to by-products and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 2 is a graph showing an X-ray diffraction pattern of a mixed powder after a heat treatment.
FIG. 3 shows Fe₂O₃FIG. 4 is a schematic diagram illustrating a reaction process in which boron nitride-coated Fe particles and the like are generated by the reaction between B and B.
FIG. 4 is a manufacturing process diagram of boron nitride-coated metal particles and boron nitride microparticles.
FIG. 5 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 6 is a schematic diagram for schematically explaining the structure of FIG. 5;
FIG. 7 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 8 is a schematic diagram for schematically explaining the structure of FIG. 7;
FIG. 9 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 10 is a graph showing an X-ray diffraction pattern of a mixed powder after heat treatment.
FIG. 11 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 12 is a schematic diagram for schematically explaining the structure of FIG. 3;
FIG. 13 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 14 is a schematic diagram for schematically explaining the structure of FIG. 5;
FIG. 15 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 16 is a schematic diagram for schematically explaining the structure of FIG. 7;
FIG. 17 is a schematic view of a tubular furnace used in the manufacturing process of Example 1.
FIG. 18 is a graph showing an X-ray diffraction pattern of the powder of the present invention.
FIG. 19 is a photograph of a particle structure according to the present invention observed with an electron microscope.
20 is a schematic diagram corresponding to the structure of the photograph of FIG.
FIG. 21 is an enlarged schematic view of a part of FIG. 20;
FIG. 22 is a flow chart and a schematic diagram for explaining the manufacturing process of the sixth embodiment.
FIG. 23 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 24 is a graph showing an X-ray diffraction pattern of a mixed powder after heat treatment.
FIG. 25 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 26 is a schematic view corresponding to the structure of the photograph of FIG. 25.
FIG. 27 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 28 is a schematic view corresponding to the structure of the photograph of FIG. 27.
FIG. 29 is a process flow and a schematic diagram for explaining the manufacturing process of the seventh embodiment.
[Explanation of symbols]
1 Fe particle, {2 BN coating, {3} lattice plane, {4} lattice plane,
5 lattice plane,
11} metal ultrafine particles, {12} α-Fe particles,
13a {13b} 13c} pattern,
14} graphite thin film boundary, {15} collodion film,
16 scale, {20 graphite thin film,
20a 20b 20c plaid,
20e plaid, {20d} plaid, {20f} plaid,
21 {21b} convex,
22 layered lattice plane,
23} dislocation, {24} lattice,
25% intermediate layer, {27} graphite growth layer,
41} mixed powder, {42} boron nitride crucible, {43} tubular furnace,
44 cleaning tank, 45 medium, 46 ultrasonic cleaning device,
47 supernatant, {48 coated metal particles,
51} mixed powder, {52} boron nitride crucible, {53} tubular furnace,
101} boron nitride microparticle, {102} cavity, {103} tube,
Section 104 {104b},
105 Cobb, {110} bend, near {111} tip,
112 @ h-BN tissue, {112b} h-BN-like site,
113 {collodion membrane, {121} mixed powder, {122} crucible,
123} tubular electric furnace, {127} supernatant, {128} boron nitride powder,
201} carbon microparticles, {202} Fe particles, {203} tubes,
203b @ tube wall,
203c {203e} tube wall,
Section 204, {205} cavity, {206} tip,
207 carbon nanoparticle, {208} Fe particle, {209} tube, {210} node,
211} cavity, {212} tube wall, {213} Fe particles,
214 Fe particles,
215 {216} raw material carbon,
217 {218} collodion membrane,
219 scale display, {220 Fe particles,
220 221 Fe main phase,
224 {227} virtual boundaries,
Phases with different orientations of the faces in the 225 array, different phases that look like pearskin patterns,
230/231/232/233/237/238/240 / graphite phase,
234 235 graphite phase,
236 239,
241} graphite phase, {242} graphite phase of other structure,
251} mixed powder, {252} boron nitride crucible, {253} tubular furnace,
254 washing tank, a solvent in which the powder after the {255} heat treatment is dispersed,
256 ultrasonic cleaning equipment, {257} supernatant, {258} carbon fine powder

Claims (32)

Metal particles obtained by reducing a metal oxide, wherein the surface of the metal particles is coated with boron nitride or carbon, and has an average particle size of 1 μm or less. . The ultrafine metal particles according to claim 1, wherein the metal oxide is an oxide containing a transition metal. The metal ultrafine particles according to claim 1, wherein a surface of the metal particles is mainly made of boron nitride having an h-BN crystal structure or carbon mainly made of graphite. 4. The ultrafine metal particles according to claim 1, wherein said boron nitride or carbon has a thickness of 100 nm or less. The metal ultrafine particle according to any one of claims 1 to 4, wherein the boron nitride or carbon has two or more layers of a lattice or lamination plane of the crystal. The ultrafine metal particles according to claim 5, wherein an intermediate phase is provided in the metal particles or in boron nitride or carbon. The main component of the metal superparticle is a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is 10% or more and less than 100% of the saturation magnetization of the magnetic metal element. Item 7. Ultrafine metal particles according to any one of Items 1 to 6. After heat treatment under the conditions of 100% humidity, 120 ° C., 1 atm, and 24 hours, the oxygen mass increment after heat treatment is 50% or less with respect to the oxygen content (mass%) before heat treatment. The ultrafine metal particles according to claim 1. A method for producing ultrafine metal particles by heat-treating a powder obtained by mixing a powder containing a metal oxide and a powder containing boron, in an atmosphere containing nitrogen,
The method for producing ultrafine metal particles, wherein the ultrafine metal particles are metal particles coated with boron nitride. The method according to claim 9, wherein the heat treatment is performed at a temperature of 800 ° C. or higher. A method for producing metal ultrafine particles by heat treating a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon, in an atmosphere containing nitrogen,
The method for producing ultrafine metal particles, wherein the ultrafine metal particles are metal particles coated with carbon. The method of claim 11, wherein the heat treatment is performed at a temperature of 600 ° C. or more. A method for producing microscopic bodies, characterized in that microparticles of boron nitride are produced by heat-treating a mixed powder of a powder containing a metal oxide and a powder containing boron in an atmosphere containing nitrogen. Method. Heat-treating a powder containing boron-containing particles and a metal oxide particle in an atmosphere containing nitrogen to obtain a product having at least one of metal particles or fine boron nitride particles. A method of manufacturing a featured micro body. The method according to claim 13, wherein the heat treatment is performed at a temperature of 800 ° C. or higher. A method of manufacturing a microparticle according to claim 13, wherein a powder having microparticles of boron nitride and metal particles is produced, and at least a part of the metal particles is removed from the powder. Method for producing microscopic bodies. A fine body produced by reducing a metal oxide in an inert gas atmosphere, which is mainly composed of boron nitride and has a wire shape or a cylindrical shape. The micro body according to claim 17, wherein the micro body has an average diameter of 0.5 µm or less. What is claimed is: 1. A cylindrical boron nitride microparticle, comprising: a portion where a ratio of an outer diameter Ro to an inner diameter Ri satisfies (Ri / Ro) ≦ 0.8. A microparticle comprising a mixture of rhombohedral boron nitride microparticles and hexagonal phase boron nitride microparticles. A microparticle characterized in that it is a microparticle of boron nitride having a rhombohedral phase and a hexagonal phase. A minute body mainly composed of boron nitride, having a cylindrical shape and having nodes or cross-links therein. A minute body comprising metal particles, a boron nitride coating covering the metal particles, and wire-shaped or cylindrical boron nitride. A method for producing a microscopic body, comprising preparing a carbon microscopic body by heat-treating a mixed powder of a powder containing a metal oxide and a powder containing carbon in an inert atmosphere. Heat treating a powder containing carbon-containing particles and metal oxide particles in an inert atmosphere to obtain a product having at least one of metal particles or carbon microparticles; How to make the body. The method according to claim 24, wherein the heat treatment is performed at a temperature of 600 ° C. or higher. 27. A method comprising producing a powder having carbon microparticles and metal particles by the method for producing microparticles according to claim 24, and removing at least a portion of the metal particles from the powder. How to make the body. A fine body produced by reducing a metal oxide in an inert gas atmosphere, which is made of graphite phase carbon and has a wire shape or a cylindrical shape. The micro body according to claim 28, wherein the micro body has an average diameter of 0.5 µm or less. What is claimed is: 1. A minute carbon body, comprising: a cylindrical carbon minute body, wherein a ratio of an outer diameter Ro to an inner diameter Ri satisfies (Ri / Ro) ≦ 0.8. A fine body mainly composed of graphite phase carbon, having a cylindrical shape and having nodes or cross-links therein. A minute body comprising metal particles, a carbon coating covering the metal particles, and wire-shaped or cylindrical carbon.

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